Optical device for filtering and sensing

Details Optical device for filtering and sensing Optical device for filtering and sensing

2002-08-06

2004-09-14

Boutsikaris, Leo (Department: 2872)

Optical: systems and elements

Light interference

Electrically or mechanically variable

C359S579000, C359S260000, C359S261000, C359S315000, C359S318000, C359S247000, C349S198000

Reexamination Certificate

active

06791757

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to an optical device that filters wavelengths of light, and can be used to sense deposited chemical or biological materials.
BACKGROUND OF THE INVENTION
In order to satisfy the bandwidth demand arising from increased use of the internet, the optical telecommunications (telecom) industry have incorporated wavelength division multiplexing (WDM) in its networks. Entirely new classes of optical devices and systems are needed to manipulate and distribute the multiple channels (defined by wavelengths of light) envisioned by optical network designers. Tunable transmitters using tunable lasers as the source, are becoming a standard replacing multiple fixed wavelength lasers. On a receiving end however, the wavelength distinction is currently accomplished by fixed wavelength, discrete components such as fiber Bragg grating filters, thin film interference filters, arrayed waveguide grating circuits, or grating based de-multiplexers. This is analogous to the early days of radio where each broadcast channel required a fixed crystal oscillator at the receiver. To produce tunable receivers for telecom networks, a suitable tunable filter technology is needed, an equivalent to radio's electronically tuned oscillator which replaced multiple channel filters with a single dynamic device.
There is an immediate need for dynamic devices which can actively tune between channels with low signal loss, combining the function of both switches and multiplexers. A tunable filter device can replace both switches and space multiplexers, yielding a reconfigurable tunable switch module.
Many approaches for producing tunable filters are under development, but few of these have the potential to be commercially accepted. Here we describe a new approach for constructing both fixed and tunable filters which has the advantage of low cost production combined with the narrow band operation and filter shape requirements of telecom.
On a new matter, optical sensors that can detect the presence and concentration of a material deposited on a surface have a great number of applications in the fields of biotechnology and chemical analysis. High sensitivity pollution sensors, for example, are typically used to detect the presence of contaminants in water supplies and in the air we breath. A wide range of benefits can be realized in the biotechnology field if a sensor could detect the concentration of viruses and bacteria in a sample of blood or identify various proteins.
Typical biological sensors (biosensors) utilize fluorescent chemical compounds which are used to “tag” various protein or DNA molecules. When such molecules are deposited onto a surface through attachment to “receptor” chemicals, the presence and concentration of the tagged chemicals can be determined by the brightness of the light emitted by the fluorescent compounds. Recently, this technique gained prominence due to the rapid sequencing of the human genome.
Fluorescence-based biosensors are limited to the extent that the fluorescent compounds used are not applicable to all materials, such as the huge number of proteins generated in the human body. In many applications, a highly sensitive detection method is needed which does not require the use of fluorescent chemical tags. Such a method can be realized using an optical resonance phenomenon such as the highly complex surface plasmon resonance (SPR). Using a surface structure resonance phenomena, the optical filters described herein can be used to produce biosensors, which can detect minute concentrations of chemicals through a shift in the wavelength of light resonated from the sensor's surface. This type of response cannot be obtained from other filtering methods such as thin-film interference filters and fiber Bragg grating filters.
SUMMARY OF THE INVENTION
One aspect of the present invention involves a guided mode resonance surface structure optical filter that does not exhibit polarization dependence. That is, an incident beam of light need not be properly oriented so that it strikes the device in a particular way for the incident light to be adjusted or tuned properly. Instead, incident light having any polarization orientation can be adjusted or tuned. This is achieved via a circular symmetry supported by an array of surface structures with various cross-sectional shapes. One or more dimensions of the surface structure can be smaller than the wavelength of light that is reflected or redirected such that no light is scattered or diffracted.
Another aspect of the present invention is directed toward providing an optical wavelength filter device for filtering wavelengths in optical telecommunications systems. Typically, a filter structure according to certain principles of the present invention experiences minimal loss due to a polarization state of incoming light. This is achieved by providing a guided-mode surface structure filter that is formed of dielectric bodies of various predetermined shapes such as cylinders or holes repeated over the surface of a substrate and arranged in a predetermined symmetrical pattern such as a honeycomb or hexagon. It is noted that the term “body” as used herein may include “holes” filled with air or some other dielectric material.
As mentioned, a honeycomb surface pattern of such bodies can provide a high degree of circular symmetry, which allows a light beam comprising a broad range of wavelengths to be filtered efficiently without undue loss caused by the polarization state of incident light. In other words, the optical device according to the present invention can be polarization independent.
Another aspect of the present invention is directed towards an optical filter having one or multiple guided-mode surface structures to reflect a narrow range of light wavelengths from a broad spectrum of incident light. A surface structure can include a body of material forming an array or field of cylindrical holes, cylinders, or other suitable shapes.
In one application, two or more guided-mode resonance surface structures can be disposed substantially parallel and opposite to each other, thus forming a resonant cavity therebetween. Light reflections from each structure provide unique filtering, thereby narrowing the wavelength range of light that is reflected off the surface.
In another application, multiple guided-mode resonance surface structures can be grouped to form more than one resonant cavity. Light reflections from each cavity provide unique filtering, and light reflections from each cavity can be weakly or strongly coupled to the other cavities, thereby narrowing and shaping the wavelength range of light that is reflected off the surface.
Another aspect of the present invention is directed towards an optical wavelength filter device optimized to meet the isolation, loss, and narrow pass bands required by optical telecommunications applications. This can be achieved by providing two or more guided-mode surface structures (polarization independent filters) disposed substantially parallel or angled with respect to each other to form the aforesaid resonant cavity. In one application, an electro-optic medium having a controllable index of refraction can be disposed within the resonant cavity to adjust which of multiple wavelengths will be transmitted or reflected. An electric field can be applied to adjust the index of refraction of the electro-optic medium. Alternatively, the surface structure or bodies can be formed of an electro-optic material.
Yet another aspect of the present invention involves utilizing liquid crystal material as an electro-optic material to effect the polarization independent operation of a dynamically tunable pass band, guided-mode surface structure optical filter. This can be achieved by effecting the alignment of the liquid crystal molecules such that in the static state, when no electric field is present, the molecules align their extraordinary refractive index axis perpendicular to corresponding surfaces in the cavity such as the columns or holes in the optical device. Such an alignme

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