Patent Application
20090168150
1. Technical Field
The present invention relates to materials and devices with optical gains, and more particular an electro-optic material with high transparency and high optical gain and electro-optic activity and devices constructed using such materials.
2. Technical Background
Since neodymium (Nd) doped yttrium aluminate garnet, Nd:Y3Al5O12, or Nd:YAG, laser material was discovered, progress in the fabrication technique (the Czochralski, or CZ method) has rapidly improved its optical quality. In recent years, lasers have been applied with remarkable success to various fields such as laser radar, material processing, and others. Only single crystals created by the CZ method, however, have been used as laser materials. It is extremely difficult to dope more than 1 at. % of Nd homogeneously as a luminescence element in a YAG single crystal, because the effective segregation coefficient of elemental Nd in the host material (the YAG single crystal) is 0.2. Nd:YAG material's producing cost and small crystal size limit the technical advance of the solid-state laser. Thus, new solid-state materials with high efficiencies and at low costs will have great impact on high power laser development.
Attempts to synthesize solid-state laser material from polycrystalline YAG ceramics have been reported, such as by A. Ikesue, et al. (“Fabrication and optical characteristics of polycrystalline Nd:YAG ceramics for solid-state laser,” Technical Digest of CLEO/Pacific Rim'95., Jul. 10˜14, 1995, p. 3.) However, synthesizing Nd:YAG laser material of polycrystalline ceramics is technically very difficult. Polycrystalline, transparent Nd:YAG ceramics were fabricated by a solid-state reaction method using high-purity Al2O3 and Y2O3 powders, because optical materials for a solid-state laser must meet extremely severe requirements. Transparent YAGs are traditionally fabricated by a two-step process: hot pressing (HP) followed by hot isostatic pressing (HIP) at 1600-1800° C. This rendered the YAG fabrication process inefficient and high-cost.
Nd:YAG laser can be worked in either continues wave (CW) or pulsed mode. To have a high peak power, pulsed mode is preferred. One common practice to generate high peak power laser pulses is a Q-switched Nd:YAG laser. Active Q-switched laser using an acoustic-optic (AO) or electro-optic (EO) Q-switch exhibits much stable performance. However, laser materials themselves lack the capability of active Q-switching.
Lead lanthanum zirconate titanate (PLZT) is a transparent ferroelectric ceramic with a perovskite crystal structure and a variety of interesting properties that make it suitable for active electro-optical devices such as optical modulators and Q-switches. Comparing to the YAG ceramics, ferroelectric PLZT ceramics are not only highly transparent in a broad wavelength range from visible to mid-wave infrared but also among the highest electro-optic coefficient materials.
Recently, there are some efforts on rare earth doped electro-optic PLZT materials. It is taught that the neodymium (Nd) doped PLZT has good transparency, good absorption and photoluminescence. However, it has not been taught a Nd doped PLZT with large electro-optic phase retardation and large optical gain and how to build a device to utilize the Nd doped PLZT ceramics.
Any material has optical losses therefore a material can be used as lossless device is needed.
One aspect of the present invention relates to a neodymium doped, transparent electro-optic gain ceramic material consisting lead, zirconium, titanium, and lanthanum.
Another aspect of the present invention relates a neodymium doped, transparent electro-optic gain ceramic material consisting lead, zirconium, titanium and lanthanum, wherein the electro-optic gain ceramic material has either a linear or a quadratic electro-optic coefficient, which could be greater than about 0.3×10−16 m2/V2 for the latter, a propagation loss of less than about 0.3 dB/mm, and an optical gain of great than 2 dB/mm at a wavelength of about 1064 nm while optically pumped by a 2 watts diode laser at a wavelength of 802 nm at 20° C.
Another aspect of the present invention relates a neodymium doped, transparent electro-optic gain ceramic material consisting lead, zirconium, titanium, and lanthanum, wherein the electro-optic gain material has either a linear or a quadratic electro-optic coefficient, which could be greater than about 0.3×10−16 m2/V2 for the latter, a propagation loss of less than about 0.3 dB/mm, and an optical gain of great than 2 dB/mm at a wavelength of about 1064 nm while optically pumped by a 2 watts diode laser at a wavelength of 802 nm at 20° C., and wherein the electro-optic ceramic material has the formula
Pb1-y-zNdyLaz (ZrxTi1-x)1-y/4-z/4O3, wherein x is between about 0.05 and about 0.95, y is between about 0.001 and about 0.05, and z is between about 0 and about 0.15. One especially preferred electro-optic gain ceramic materials of the present invention, x is between about 0.55 and about 0.85, y is between about 0.001 and about 0.03, and z is between about 0.07 and 0.12.
Another aspect of the invention is an electro-optic device including a neodymium doped, lead, zirconium, titanium, and lanthanum-based electro-optic gain ceramic material.
Yet another aspect of the invention is a lossless electro-optic device or an optical amplifier including a neodymium doped lead, zirconium, titanium, and lanthanum-based electro-optic gain ceramic.
The materials and devices of the present invention result in a number of advantages over conventional materials and devices. The materials of the present invention have high transparency over a wide wavelength range. The materials have significant quadratic electro-optic coefficients and high optical gains make it suitable for both electro-optic device and laser applications. Additional features and advantages of the invention will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from the description or recognized by practicing the invention as described in the written description and claims hereof, as well as in the appended drawings.
It is to be understood that both the foregoing general description and the following detailed description are merely exemplary of the invention, and are intended to provide an overview or framework to understanding the nature and character of the invention as it is claimed.
The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings are not necessarily to scale. The drawings illustrate one or more embodiment(s) of the invention, and together with the description serve to explain the principles and operation of the invention.
The present invention provides an electro-optic gain ceramic material with high transparency, high quadratic electro-optic coefficients, and high optical gain. The electro-optic gain ceramic materials of the present invention are rare earth neodymium ion (Nd3+) doped lanthanum-modified lead zirconate titanate (PLZT) ceramics having either a linear or a quadratic electro-optic coefficient, which could be greater than about 0.3×10−16 m2/V2 for the latter, a propagation loss of less than about 0.14 dB/mm, and an optical gain of great than 2 dB/mm at a wavelength of about 1064 nm while optically pumped by a 2 watts diode laser at a wavelength of 802 nm at 20° C. The electro-optic gain ceramic materials of the present invention are useful in the fabrication of electro-optic devices such as optical amplifiers and ceramic lasers. It is also useful for various electro-optic devices such as modulators, switches, polarization controllers, and variable optical attenuators. These devices could be a optically lossless device under appropriate optical pumping.
Electro-optic materials are materials that change their birefringence in the presence of an electric field. The utility of an electro-optic material in an electro-optic device depends, in large part, on the magnitude of its electro-optic coefficients. The birefringence Δn of an electro-optic material in the presence of an electric field can be described by the equation
where Δn0 is the birefringence of the material in the absence of an electric field, n is the ordinary refractive index of the material, E is the magnitude of the applied electric field, γ is the linear electro-optic coefficient, and R is the quadratic electro-optic coefficient. As the electro-optic gain ceramic materials of the present invention, a Nd3+ doped PLZT (Nd:PLZT) electro-optic gain ceramic materials may exhibit either linear electro-optic coefficient γ after electrical poling or quadratic electro-optic coefficients R, depending on the materials composition ratio. One example of the present invention is the Nd:PLZT electro-optic gain ceramic material is isotropic under no external electric field, Δn0 and γ are essentially zero, making the electro-optic activity proportional to the quadratic electro-optic coefficient. The Nd:PLZT electro-optic gain ceramic materials described herein as the example have quadratic electro-optic coefficients R greater than about 0.3×10−16 m2/V2 at 20° C. and at a wavelength of 1064 nm.
While electro-optic activity is important, a material with high electro-optic activity will be rendered useless if it is not sufficiently transparent at the wavelength of interest. Transparency at wavelengths ranging from visible to infrared is an important feature of the electro-optic gain ceramic materials of the present invention. As will be described more fully below, the electro-optic ceramic gain materials of the present invention can be formed by the skilled artisan to be very dense and relatively free of scattering voids and undesired impurity phases. The electro-optic gain ceramic materials of the present invention have propagation losses of less than about 0.3 dB/mm, and preferably less than about 0.14 dB/mm.
In the present invention, the electro-optic gain ceramic material includes lead, zirconium, titanium, lanthanum and neodymium. The relative amounts of individual atomic species may be described by a cation fraction. As used herein, a cation is any atomic species bearing a positive formal charge. For example, though the titanium atom is part of the polyatomic titanium anion (TiO32−) in the present compositions, the titanium atom itself has a +4 formal charge, and is thus considered herein to be a cation. The cation fraction of a particular atomic species is the ratio of the number of atoms of the particular atomic species to the total number of cationic atoms.
In the electro-optic gain ceramic materials of the present invention, each crystalline grain desirably has a perovskite structure. The perovskite structure, shown in
Preferred electro-optic gain ceramics of the present invention may be described by the general formula
Pb1-y-zNdyLaz(ZrxTi1-x)1-y/4-z/4O3
wherein x is between about 0.05 and about 0.95, y is between about 0.001 and about 0.05, and z is between about 0 and about 0.15. In especially preferred electro-optic gain ceramic materials of the present invention, x is between about 0.55 and about 0.85, y is between about 0.001 and about 0.03, and z is between about 0.07 and 0.12.
The electro-optic gain ceramic materials of the present invention may be made by methods familiar to the skilled artisan. A wide variety of inorganic compounds may be used as the starting materials. For example, oxides, hydroxides, carbonates, sulfates, acetates or alkoxides of the desired metals may be used to form the ceramics of the present invention. In general, an opaque powder having the desired ceramic stoichiometry is first prepared and dried. For example, the mixed oxide method has been used to fabricate powders of the materials of the present invention, as described below in Example 1. Other methods, such as chemical co-precipitation and other more advanced techniques, may be used to prepare the powder. Before being densified, the powder may optionally be formed into an opaque powder preform by, for example, cold pressing.
The opaque powder or powder preform may then densified by methods familiar to the skilled artisan to form the ceramic materials of the present invention. For example, a powder preform may be hot-pressed to form a dense, transparent, perovskite-structured ceramic as described below in Example 1. Important processing parameters such as hot-pressing temperature, applied pressure, ambient conditions and processing time may be determined by the skilled artisan. Other densification techniques, such as vacuum sintering, isostatic pressing, hot isostatic pressing, or other pressing or sintering methods may be used by the skilled artisan to form the transparent ceramics of the present invention.
The electro-optic gain ceramic materials of the present invention are useful in the construction of electro-optic devices. Another aspect of the invention is an electro-optic device including a neodymium doped lead, zirconium, titanium and lanthanum-based electro-optic gain ceramic material. The electro-optic device may work at a wavelength in the range of 500 nm to 2600 nm. The electro-optic gain material used in the device may have a quadratic electro-optic coefficient of greater than about 0.3×10−16 m2/V2, a propagation loss of less than about 0.3 dB/mm, and an optical gain of great than 2 dB/mm at 20° C. at a wavelength of 1064 nm. The electro-optic ceramic material used in the device may have the compositions described hereinabove. The electro-optic gain ceramic material has the general formula Pb1-y-zNdyLaz(ZrxTi1-x)1-y/4-z/4O3 wherein x is between about 0.05 and about 0.95, y is between about 0.001 and about 0.05, and z is between about 0 and about 0.15. In especially preferred electro-optic gain ceramic materials of the present invention, x is between about 0.55 and about 0.85, y is between about 0.001 and about 0.03, and z is between about 0.07 and 0.12.
An electro-optic device of the present invention may be, for example, an intensity modulator, a phase modulator, a switch, a phase retarder, a polarization controller, or a variable optical attenuator. Exemplary electro-optic devices that may be constructed using the electro-optic gain ceramic material of the present invention are described in U.S. Pat. Nos. 6,137,619, 6,330,097, 6,404,537, 6,522,456, and 6,700,694. Electro-optic devices of the present invention may be constructed in accordance with known techniques for making devices based on other electro-optic materials, such as PLZT.
Yet another aspect of the present invention relates to an optical lossless device or a light amplifier using a neodymium doped electro-optic gain ceramic material including lead, zirconium, titanium, and lanthanum. The operating wavelength is in the range of 1040 nm to 1100 nm.
The invention will be further clarified by the following non-limiting examples which are intended to be exemplary of the invention.
A electro-optic gain ceramic material, 0.5% Nd:PLZT having the formula
Pb0.895Nd0.005La0.10(Zr0.65Ti0.35]0.9738O3
The 0.5 at. % Nd3+ doped PLZT 10/65/35, or 0.5% Nd:PLZT, consisted of 65 mol % lead zirconate plus 35 mol % lead titanate and 10 mol % lanthanum in the form of La2O3, i.e. 10/65/35, to which 0.5 mol % Nd cations had been added in the form of Nd2O3. The origins of the components were PbO, La2O3, ZrO2, TiO2, and Nd2O3, respectively. Raw materials (oxide powders) were weighed and mixed according to batch formulation. It was followed by a 900° C., 1-hour calcination reaction. The calcined powders were then ball-milled to yield the final powder of fine particle size, which is then ready to be hot-pressed. Prepared powders were cold-pressed into a preform with a diameter of 1.25-4 inches under a pressure of 2,500 psi. During the hot press stage, a pressure of 1,000-3,000 psi was applied through two alumina rods in a temperature-controlled furnace. The firing was carried out at 1100-1300° C. for up to 20 hrs under an oxygen atmosphere. The fired slug was then cut and polished into wafers for various analyses. Different percentage of Nd3+ doping may be made by the skilled artisan. 0% to 3% Nd3+ doped PLZT had been made.
X-ray diffraction patterns are measured for un-doped PLZT, 0.5% Nd:PLZT, and 1% Nd:PLZT, respectively, using a Rigaku diffractometer with CuKα radiation in the 2θ range of 15° to 75° as shown in
The transmission of both the 0.5% Nd:PLZT and 1% Nd:PLZT samples with a thickness of 2 mm are found to be very similar and is around 70% in the wavelength range from 500 nm to 2600 nm as shown in
The quadratic electro-optic constant of the 0.5% Nd:PLZT and 1.0% Nd:PLZT material of Example 1 was measured using the experimental setup shown in
When no electric field is applied, the sample 44 has no effect on the polarization of the beam; therefore, no light makes it to the detector due to the action of the crossed polarizers 42 and 43. As the applied electric field increases, the sample becomes birefringent due to the electro-optic effect, and rotates the polarization of the beam. At a voltage Vπ, the polarization of the beam is rotated by the sample enough to be parallel to the polarization axis of the second polarizer 43, maximizing the intensity of the detected signal. Assuming the material's native birefringence (Δn0) and linear electro-optic coefficient γ are zero, the quadratic electro-optic coefficient R may be calculated from the equation
where d is the distance between electrodes (i.e. the width of the sample), n is the refractive index of the sample at the wavelength λ, and L is the path length of the beam in the sample.
Samples were cut from a 1.44 mm thick wafer polished on both sides. The samples had a width of 0.5 mm and a height of 2.5 mm. The parallel side surfaces of each sample were polished, plasma etched for 3 min, then coated with Pt/Au electrodes (250 Å/2500 Å). The electric field induced phase retardation of 0.5% Nd:PLZT and 1% Nd:PLZT was illustrated in
The room temperature ground state absorbance of 1% Nd3+ doped PLZT from Example 1 was measured in spectral region of 400˜1000 nm by a UV-VIS-NIR spectrophotometer (Perkin-Elmer, Lamda 9). A number of absorption lines are observed and assigned as transitions from the Nd3+ ground state 4I9/2 to different excited states, namely 4F3/2 (879 nm), 4F5/2 (803 nm), 2H9/2 (803 nm), 4F7/2 (742 nm), 4S3/2 (742 nm), 4F9/2 (681 nm), 2H11/2 (629 nm), 4G5/2 (585 nm), 2G7/2 (585 nm), 4G7/2 (526 nm), 2G9/2 (514 nm), and 4G9/2 (475 nm), as shown in
The room temperature photoluminescence (PL) was measured using a CW diode laser as the excitation source (LDI 820). The PL was obtained with excitation of levels 2H9/2 and 4F5/2 at 798 nm because the absorption coefficient at this wavelength was at least three times higher than that corresponding to 4I9/2→4F3/2 transition at 870 nm, as shown in
A configuration resembling to a traditional two-wave mixing geometry was chosen in our single-pass gain measurements, as shown on
Very high single-pass gains have been obtained in both the 1.0% Nd:PLZT and 0.5% Nd:PLZT samples from Example 1. For a fixed seed power 50 nW with 1.0 mm diameter of the seed laser beam, the gains as a function of pumping power for the samples were shown in
Electro-optic device can be configured which includes a neodymium doped, lead, zirconium, titanium and lanthanum-based electro-optic gain ceramic material. The Nd:PLZT is transparent from 500 nm to 2600 nm. Various electro-optic devices can be constructed using this material. Some examples are a light modulator, a light polarization transformer/controller, an optical filter, an optical switches and an optical retarder.
Since the optical gain is much greater than the loss, a lossless electro-optic device or an optical amplifier can be constructed. Illustrated in
The wavelength of the optical pumping source is in the range of 794 nm to 810 nm. The device is preferred working at a wavelength in the range of 1040 nm to 1100 nm, for both a lossless device and an optical amplifier.
It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit and scope of the invention. Thus, it is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.
This is a division of application Ser. No. 11/528,166, filed Sep. 27, 2006, which claims the benefit of Provisional Patent Application Ser. No. 60/812,263 filed Jun. 9, 2006, the entire teachings of all of which are incorporated herein by this reference.
This invention was made with Government supports under grant no. DMI-0450547 awarded by National Science Foundation. The government has certain rights in this invention.
| Number | Date | Country | |
|---|---|---|---|
| 60812263 | Jun 2006 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11528166 | Sep 2006 | US |
| Child | 12365150 | US |
