Ultra high density disk reader/writer comprising two interferometers

Abstract

An optical apparatus for reading from and writing to an ultra high density disk and comprising a light source emitting a pencil of light rays to an optical path along an optical axis; two interferometers, a beamsplitter, a quarter-wave plate, and an objective lens. The pencil of light rays is transmitted through the apparatus to become a narrow fringe ring which in turn is used to generate an ultra small spot of light. The resulting ultra small spot of light can address far more storage locations per a same unit area than a conventional much larger spot of light.

Description

BACKGROUND OF THE INVENTION

The technological growth of the computer industry has been progressing at an extremely fast pace. Products that are barely three years old are considered obsolete. The demand for more powerful computers translates into demands of faster data processing speed and greater data storage capacity. The present invention fits in the category of meeting the demand for greater data storage capacity. Presently, data stored on an optical data it storage device are retrieved by observing the behavior of light being reflected from the optical data storage device. As storage capacity increases, the amount of data per unit of area increases. A practical limitation of the storage capacity of an optical data storage device is the size of a spot of light that can be generated by a reader/writer head and the technology available to precisely move and control its position. The present invention discloses a spot of light that is considerably smaller than those currently being used in the market place.

SUMMARY OF THE INVENTION

The present invention discloses a novel method and apparatus to produce an extremely small spot of light and electronically control its position.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a first embodiment of an optical configuration using a Fabry-Perot interferometer and a spectral light source.

FIG. 2 illustrates an annular constructive interference fringe rings produced by the first embodiment as shown in FIG. 1 .

FIG. 2 a illustrates an intensity distribution of the constructive interference fringes in a focal plane.

FIG. 3 illustrates a second embodiment of an optical configuration using a Fabry-Perot interferometer and a spectral light source.

FIG. 4 illustrates an annular constructive interference fringe rings produced by the second embodiment as shown in FIG. 3 .

FIG. 5 illustrates a third embodiment of an optical configuration using two Fabry-Perot interferometers and a spectral light source.

FIG. 6 illustrates two annular constructive interference fringe rings produced by the third embodiment as shown in FIG. 5 .

FIG. 7 illustrates a Fabry-Perot interferometer configured as an electro-optical device containing a media inside the interferometer that exhibits Kerr or Pockel effect.

FIG. 8 illustrates a first embodiment of an ultra high density optical disk reader/writer.

FIG. 9 illustrates a second embodiment of an ultra high density optical disk reader/writer.

FIG. 10 illustrates a third embodiment of an ultra high density optical disk reader/writer.

FIG. 11 illustrates a mechanism employed to electronically control the location of the ultra small spot of light.

DETAIL DESCRIPTION OF THE INVENTION

FIG. 1 shows an optical system employing a conventional Fabry-Perot interferometer. The Fabry-Perot interferometer is an angle filter and is the basis of this invention.

In FIG. 1 , the X-axis is parallel to an optical axis 395 of the Objective lens 300 . The Y-axis lies in a plane of the drawing and is perpendicular to axis 395 . The Z-axis is perpendicular to the plane of the drawing.

A spectral light source 100 emits a pencil of light rays 190 . The central ray 195 of pencil 190 , is incident upon a Fabry-Perot interferometer 210 , in a direction normal to entrance face 211 as figuratively illustrated by a broken line 212 . Central ray 195 is parallel to an optical axis 395 of the Objective lens 300 .

It is a long established principal of multiple-beam interference phenomenon, well known to those skilled in the art of physical optics, that of the infinite number of light rays incident upon a Fabry-Perot interferometer, only those having angles normal to the entrance face 211 can successfully transited through the interferometer. All other light rays suffer destructive interference thus are filtered out.

Those light rays successfully transmit through interferometer 210 are collected by Objective lens 300 , to be converged into annular constructive interference fringe rings on a focal plane 400 . These annular constructive interference fringe rings are shown in FIG. 2 . The central fringe 500 is shown at the focal point of lens 300 with a first annular ring fringe 510 located at a radius r 1 from the central fringe 500 . r 1 is defined as:

r 1 =arctan(θ1/f)

where θ1 is an angle relative to the normal broken line 212 inside pencil 190 , and f is a focal length of lens 300 . Likewise r 2 , the radius of the second annular ring fringe, 520 , and r 3 , the radius of the second annular ring fringe 530 , are defined as:

r 2 =arctan(θ2/f); and

r 3 =arctan(θ3/f).

FIG. 2 a shows the relation between these radii, angles, and lens 300 and focal plane 400 . Angles θ1, θ2, and θ3 are defined by a design of the interferometer as shown in a sample calculation included hereinbelow.

It should be noted that the closer is the fringe to the focal point of lens 300 , the wider is the fringe. Conversely, the farther is a fringe from the focal point of lens 300 , the narrower is the fringe. Since FIG. 2 is drawn on white paper, the colors are reversed. The black rings actually represent high intensity constructive interference fringe rings and the white spacing therebetween represent regions void of light, also known as a regions of destructive interference where light rays have been filtered out of pencil 190 .

The second embodiment of an optical configuration using a Fabry-Perot interferometer and a spectral light source is shown in FIG. 3 . This is a modification of FIG. 1 wherein interferometer 210 has been rotated by an angle θ1 about the Z-axis. This causes fringe 510 to be displaced in focal plane 400 along the Y-axis by a distance r 1 , as shown in FIG. 4 .

The third embodiment of an optical configuration using two Fabry-Perot interferometers and a spectral source is shown in FIG. 5 . This is a modification of FIG. 3 wherein a second Fabry-Perot interferometer 220 has been added. For the sake of clarity, the fringe that would be transmitted by interferometer 210 is labeled as 510 a while those that would be transmitted by interferometer 220 are labeled as 510 b.

Interferometer 220 has been rotated by an angle θ1 about the Y-axis and interferometer 210 has been rotated by an angle θ1 about the Z-axis. This causes fringe 510 a to be displaced in the focal plane of lens 300 , along the Y-axis by a distance r 1 , and fringe 510 b to be displaced in the focal plane of lens 300 , along the Z-axis by a distance r 1 , as shown in FIG. 6 .

Because interferometer 210 can only permit transmission of light rays making an angle θ1 with respect to the normal broken line 212 and interferometer 220 can only transmit rays making an angle θ1 with respect to the normal broken line 212 , spots only appear in the focal plane when these conditions are met. A preferred spot is located at the focal point of lens 300 . A complimentary spot lies diagonally bisecting the Y-axis and Z-axis. The complimentary spot is masked out.

The Fabry-Perot interferometer is only one member out of a family of instruments that employ the principals of multiple-beam interference. Other members of this family include the Lummer-Gehrcke interferometer, the interference filter, and the frustrated total reflection interference filter. All of these instruments regenerate every single light ray, from a pencil of light rays, into a multitude of parallel, geometrically degraded amplitude, phase related light rays. When a set of parallel rays are brought to separate points in the focal plane of a lens, they M will interfere with each other. The intensity of the light ray at each point depends on the number of optical paths between sequential parallel plates the light ray has traveled. If the path difference between sequential sets of rays is an integer number of wavelengths, then the intensity is at a maximum. If it is a half integer, the intensity is zero. Any other value of the path difference will yield an intermediate intensity.

Thus, in addition to the Fabry-Perot interferometer, this invention will function with either a Lummer-Gehrcke interferometer, an interference filter, or a frustrated total reflection interference filter.

FIG. 7 illustrates by way of an example a Fabry-Perot interferometer functioning as an electro-optical device employing the Kerr or Pockel effect. It should be noted that the electro-optical device can also be a Lummer-Gehreke interferometer, interference filter, or frustrated total reflection interference filter. The medium inside the Fabry-Perot interferometer, Lummer-Gehreke interferometer, interference filter, or frustrated total reflection interference filter can be an electro-optical material so that a voltage applied across therein will change an index of the medium thus causing angles that can propagate through the instrument to change. The medium can be various types of gases, liquids or solids, such as KD*P.

A design sample showing detailed calculations and designed parameters are included hereinbelow. As shown, the total number of bytes that can be easily generated by the present invention is in the order of 109.1 giga bytes on a 120-millimeter diameter disk.

If the medium between the reflecting surfaces is an electro-optical material, then the optical path changes when an electric or magnetic field is applied therethrough. This changes the angle of constructive interference, thus changing the location of the spot, or constructive interference fringe on focal plane 400 .

A magnetic or electric field applied to the spectral source changes the wavelength of the source. This also changes the location of the spot on focal plane 400 . It is desirable for the optical apparatus for reading information from and writing information to a data storage device to comprise: (a) a light source emitting a pencil of light rays to an optical path along an optical axis; (a) an interferometer; (c) a beamsplitter; (d) a quarter wave plate; and (e) an objective lens; wherein the pencil of light rays is transmitted respectively through the interferometer, the beamsplitter, the quarter-wave plate, and the objective lens to become constructive interference fringes of light upon reaching the data storage device and wherein the light source is a laser diode and the spectral source resides inside an electric field so that the wavelength of the pencil of light rays are Stark split into a plurality of wavelengths.

Additional embodiments of the apparatus of the present invention include an optical apparatus for reading information from and writing information to a data storage device, comprising: (a) a light source surrounded by a coil generating either an electric field or a magnetic field and emitting a pencil of light rays to an optical path along an optical axis; ˜(b) an interferometer; and (c) an objective lens and wherein the pencil of light rays is transmitted respectively through the interferometer and objective lens to become constructive interference fringes of light upon reaching said field-controlled location on a focal plane of the objective lens and wherein the light source is a laser diode with the spectral source residing inside an electric field so that a wavelength of the pencil of light rays are Stark split into a plurality of wavelengths.

Various embodiments of the ultra high density optical disk readers as shown in FIG. 8 , FIG. 9 , and FIG. 10 are correspondingly based on various embodiments of ultra small spot generators as shown in FIG. 1 , FIG. 3 and FIG. 5 .

FIG. 8 illustrates a read/write optical head wherein a spot in the focal plane of a lens is illuminated and characteristics of reflected light rays are detected. Here, source 100 emits a diverging pencil 190 , polarized in the plane of the drawing, which is transmitted through Fabry-Perot interferometer 210 , polarizing beam splitter 250 , quarter-wave plate 260 , and lens 300 to produce spot 500 on focal plane 400 . The quarter-wave plate rotates the polarization, about the optical axis by 45 degrees.

When spot 500 is reflected from focal plane 400 , the light rays return through lens 300 as a converging pencil into the quarter-wave plate 260 . Quarter-wave plate 260 rotates the polarization about the optical axis by an additional 45 degrees so that it is now perpendicular to the plane of the drawing. Thus the pencil of light rays will be totally reflected as they pass through polarizing beam splitter 250 . These light rays are then passed through lens 600 onto a photon detector 700 .

FIG. 9 is the same as FIG. 8 except Fabry-Perot interferometer 210 has been rotated by an angle θ1 about the Z-axis.

FIG. 10 is the same as FIG. 9 except an additional Fabry-Perot interferometer 220 has been added. Interferometer 220 has been rotated by an angle θ1 about the Y-axis and interferometer 210 has been rotated by an angle θ1 about the Z-axis.

FIG. 11 illustrates a mechanism that electronically controls the location of the ultra small spot of light on the focal plane 400 . Source 100 is subjected to a coil 103 generating a magnetic field parallel to the optical axis of lens 300 . This causes the wavelength of these light rays to split into multiple wavelengths. Ideally, there would be two wavelengths. A set of rays with one wavelength would be right circularly polarized and a set of rays with another wavelength would be left circularly polarized. The separation of these wavelengths is a function of the intensity of the magnetic field.

Both sets of light rays pass through a quarter-wave plate 150 that is constructed of a material with Kerr or Pockel effects. Thus, by impressing a specific electric field on plate 150 , both sets of circularly polarized rays become linearly polarized. For example, the right circularly polarized light will become linearly polarized in the plane of the drawing and the left circularly polarized light will become linearly polarized perpendicular to the plane of the drawing.

These rays are then transmitted through polarizing filter 160 where one ray is filtered out.

Thus, by changing the intensity of the electric field on plate 150 , the wavelength of the rays being transmitted by interferometer 210 and interferometer 220 is changed. This in turn will cause the constructive interference fringe of ultra small spot of light to appear at different locations of focal plane 400 .

By adjusting the intensity of the magnetic field at source 100 , the wavelength of the Zeeman split light ray can be adjusted to equal the pit width. The spot can then be made to oscillate from one side of a target to another by oscillating the electric field on quarter-wave plate 150 . Thus, the intensity of the signal at detector 700 will define the magnitude of any difference between where the spot should be and the pit and its phase will define the direction of the error.

From the foregoing detailed description, it will be evident that there are a number of changes, adaptations and modifications of the present invention which come within the province of those persons having ordinary skill in the art to which the aforementioned invention pertains. However, it is intended that all such variations not departing from the spirit of the invention be considered as within the scope thereof as limited solely by the appended claims.

Sample calculations of the present invention are shown hereinbelow.

Fabry-Perot Configured ETOS (FPCD.mcd)
Wavelength of the laser	λ := 0.635 microns
Focal length of the objective lens	f := 1000.000 microns
Index of refraction of the Fabry-Perot (KD*P)	n := 1.502
Numerical aperture of the objective lens	NA := 0.45
Diameter of the objective lens	D := 2 · f · NA	D = 900 microns
Radius of the 3db intensity contour	r3db := 0.446 microns
Design objectives (based on the intensity contours used by the DVD System)
If the principal constructive interference fringe is at the center of the pit being read then
Ipw = intensity of the maximum circle inside the pit	Ipw := 0.811
Ipl = intensity of the circle encompassing the minimum pit	Ipl := 0.695
Ias = intensity at the center of the adjecent spiral	Ias := 0.257
The first constructive interference fringe ring [order of interference (M − 1)]
Radius in the focal plane	r1 := 15 microns
Angle with respect to the optical axis	$$ θ1 := atan ⁡ ( r1 f )	θ1 = 0.014999 radians
Transmission angle through the Fabry-Perot	$$ φ1 := asin ⁡ ( sin ⁡ ( θ1 ) n )	φ1 = 0.009986 radians
Interferometer configuration parameters
Order of interference	$$ M := floor ⁡ ( 1 1 - cos ⁡ ( φ1 ) )	M = 20057
		sin(M · π) 2 = 0
		sin((M − 0.5) · π) 2 = 1
		sin((M − 1) · π) 2 = 0
Thickness of the Fabry-Perot Interferometer	$$ T := M · λ 2 · n	T = 4.24 · 10 3 microns
$$ θ3db := atan ⁡ ( r3db f )	θ3db = 0.000446
$$ φ3db := asin ⁡ ( sin ⁡ ( θ3db n ) )	φ3db = 0.000297
$$ M3db := 2 · T · n · cos ⁡ ( φ3db ) λ	M3db = 2.0057 · 10 4	sin(M3db · π) 2 = 7.717 · 10 −6
Coefficient of reflection	R := 0.95	R = 0.95
Intensity distribution constance	$$ F := 4 · R ( 1 - R ) 2	F = 1.52 · 10 3
The second constructive interference fringe ring [order of interference (M − 2)]
Transmission angle through the Fabry-Perot	$$ φ2 := acos ⁡ ( M - 2 M )	φ2 = 0.014 radians
Angle with respect to the optical axis	θ2 := asin(n · sin(φ2))	θ2 = 0.021 radians
Radius in the focal plane	r2 := f · tan(θ2)	r2 = 21.216 microns
The third constructive interference fringe ring [orede of interference (M − 3)]
Transmission angle through the Fabry-Perot	$$ φ3 = acos ⁡ ( M - 3 M )	φ3 = 0.017 radians
Angle with respect to the optical axis	θ3 := asin(n · sin(φ3))	θ3 = 0.026 radians
Radius in the focal plane	r3 := f · tan(θ3)	r3 = 25.986 microns
Radial distribution (from the center of the fringe) of the intensity at the surface of the disk
i := 0, 1 . . . 2000
$$ r i := r1 · i 1000
$$ θ i := atan ⁡ ( r i f )	$$ φ i := asin ⁡ ( sin ⁡ ( θ i ) n )	$$ δ i := 4 · π · n · T · cos ⁡ ( φ i ) λ	$$ I i := 1 1 + F · sin ⁡ ( δ i 2 ) 2
$$ δr := r1 1000
Radial distribution of the intensity of the Central fringe
I3db i := if(I i < 0.5, 0, 1)
Opertional Fringe Intensity distribution at the surface of the disk
j := 0, 1 . . . 2000
$$ r j := 10 + j 200
$$ θ i := atan ⁡ ( r i f )	$$ φ i := asin ⁡ ( sin ⁡ ( θ i ) n )	$$ δ i := 4 · π · n · T · cos ⁡ ( φ i ) λ	$$ I j := 1 1 + F · sin ⁡ ( δ j 2 ) 2
Opertional fringe intensity factors
pit j := if(I j < Ipw, 0, 1)	mpl j := if(I j < Ipl, 0, 1)	pitch j := if(I j < Ias, 0, 1)	microns
Sampleling interval	$$ Δ := r 2000 - r 0 2000	Δ = 0.005 microns
Fringe parameters
3db Beam width:	I j := I j	hpp j := if(I j < 0.5, 0, 1)	half power points
	$$ BW := Δ · ∑ j ⁢ hpp j	$$ ∑ j ⁢ hpp j = 25	BW = 0.125 microns
Pit width:	$$ pw := Δ · ∑ j ⁢ pit j	$$ ∑ j ⁢ pit j = 11	pw = 0.055 microns
Minimum pit length:	$$ pl := Δ · ∑ j ⁢ mpl j	$$ ∑ j ⁢ mpl j = 17	pl = 0.085 microns
Pitch of the spiral:	$$ pch := 0.5 · Δ · ∑ j ⁢ pitch j	$$ ∑ j ⁢ pitch j = 41	pch = 0.1025 microns
Disk storage
ro = outer radius of the data storage ring	ro := 5.8 · 10 4 microns
ri = inter radius of the data storage ring	ri := 2.5 · 10 4 microns
ns = number of data spirls (revolutions of the disk)	$$ ns := ro - ri pch	ns = 3.22 · 10 5 revolutions
ls = length of the data spiral	ls := π · ns · (2 · ri | (ns 1) · pch)
	ls = 8.395 · 10 10 microns
nlpp = number of “land/pit” pairs in the data spiral	$$ nlpp := ls 2 · pl	nlpp = 4.938 · 10 11
btp = bytes to pits conservision	btp := 0.221
tnb = total number of bytes	tnb := nlpp · btp	tnb = 1.091 · 10 11 bytes
Physical Constances
C = speed of light (microns/second)		C := 3 · 10 14
r = electro-optic coefficient (microns/volts)		r = 3.22 · 10 −5
ε = dielectric constant:		ε := 44.5
kZ = Zeeman constant	kZ := 7.142857 · 10 −7 · C	kZ = 2.143 · 10 8
$$ pr := pw 2	pr = 0.0275	pch = 0.103
$$ θhpw := atan ⁡ ( r1 - pr f )	θ1 = 0.014999 θhpw = 0.014971	$$ θpch := atan ⁡ ( r1 - pch f )	θpch = 0.014896
$$ φhpw := asin ⁡ ( sin ⁡ ( θbpw ) n )	φ1 − 0.009986 φhpw = 0.009967	$$ φpch := asin ⁡ ( sin ⁡ ( θpch n ) )	φpch = 0.009918
$$ nhpw := ( M - 1 ) · λ 2 · T · cos ⁡ ( φhpw )	nhpw = 1.501999724	$$ npch := ( M - 1 ) · λ 2 · T · cos ⁡ ( φpch )	npch = 1.501998982
$$ Vhpw := 2 · ( n - nhpw ) · T r · n 3	Vhpw = 21.427	$$ Vpch := 2 · ( n - npch ) · T r · n 3	Vpch = 79.126
$$ λhpw := 2 · T · n · cos ⁡ ( φhpw ) M - 1	λhpw = 0.635000117	$$ λpch := 2 · T · n · cos ⁡ ( φpch ) M - 1	λpch = 0.63500043
λlhpw := 2 · λ − λhpw	λlhpw = 0.634999883	λlpch := 2 · λ − λpch	λlpch = 0.63499957
$$ Hfppw := kZ · ( 1 λ - 1 λhpw )	Hfppw = 61.944	$$ Hpch := kZ · ( 1 λ - 1 λpch )	Hpch = 228.753

Claims

1. An optical apparatus for reading information from and writing information to a data storage device, comprising:a light source emitting a pencil of light rays to an optical path along an optical axis; a first interferometer; a second interferometer; a beamsplitter; a quarter wave plate; and an objective lens; wherein the pencil of light rays is transmitted respectively through the interferometer, the beamsplitter, the quarter-wave plate, and the objective lens to become constructive interference fringes of light upon reaching the data storage device.

2. The optical apparatus of claim 1, wherein the first and second interferometers are in optical alignment to the optical axis.

3. The optical apparatus of claim 1, wherein the first interferometer has a first interferometer optical axis intersecting the optical axis.

4. The optical apparatus of claim 3, wherein the second interferometer has a second interferometer optical axis intersecting the optical axis.

5. The optical apparatus of claim 4, wherein the data storage device is in a focal plane of the objective lens.

6. The optical apparatus of claim 1, wherein a plane defined by the first interferometer optical axis and the optical axis perpendicularly intersects a plane defined by the second interferometer optical axis and the optical axis.

7. The optical apparatus of claim 1, wherein the pencil of light rays is filtered by the first interferometer to produce a definable number of constructive interference fringe rings all sharing a center point and each ring has a unique radius as measured from the center point.

8. The optical apparatus of claim 7, wherein the pencil of light rays that are filtered by the first interferometer and the second interferometer becomes a sector as manifested on a focal plane of the objective lens.

9. The optical apparatus of claim 1, wherein one of or both of the first and second interferometers are Fabry-Perot interferometers.

10. The optical apparatus of claim 9, wherein one of or both of the first and second Fabry-Perot interferometers are electro-optical devices containing a medium that exhibits one of a Kerr effect and a Pockel effect.

11. The optical apparatus of claim 1, wherein one of or both of the first and second interferometers are Lummer-Gehrcke interferometers.

12. The optical apparatus of claim 11, wherein one of or both of the Lummer-Gehrcke interferometers are electro-optical devices containing a medium that exhibits one of a Kerr effect and a Pockel effect.

13. The optical apparatus of claim 1, wherein one of or both of the first and second interferometers are interference filters.

14. The optical apparatus of claim 13, wherein one of or both of the first and second interference filters are electro-optical devices containing a medium that exhibits one of a Kerr effect and a Pockel effect.

15. The optical apparatus of claim 1, wherein one of or both of the first and second interferometers are frustrated total interference filters.

16. The optical apparatus of claim 15, wherein one of or both of the first and second frustrated total interference filters are electro-optical devices containing a medium that exhibits one of a Kerr effect and a Pockel effect.

17. The optical apparatus for reading information from and writing information to a data storage device, comprising:a light source surrounded by a coil generating either an electric field or a magnetic field and emitting a pencil of light rays to an optical path along an optical axis; a first interferometer; a second interferometer; and an objective lens; wherein the pencil of light rays is transmitted respectively through the first and second interferometer and objective lens to become constructive interference fringes of light upon reaching said field-controlled location on a focal plane of the objective lens.

18. The optical apparatus of claim 17, wherein the first and second interferometers are in the optical path.

19. The optical apparatus of claim 17, wherein the first interferometer has a first interferometer optical axis intersecting the optical axis.

20. The optical apparatus of claim 17, wherein the second interferometer has a second interferometer optical axis intersecting the optical axis.

21. The optical apparatus of claim 17, wherein a plane defined by the first interferometer optical axis and the optical axis perpendicularly intersects a plane defined by the second interferometer optical axis and the optical axis.

22. The optical apparatus of claim 17, wherein the pencil of light rays is filtered by the first interferometer to produce a definable number of constructive interference fringe rings all sharing a center point and each ring has a unique radius as measured from the center point.

23. The optical apparatus of claim 22, wherein the pencil of light rays filtered by the first interferometer and the second interferometer becomes a sector as manifested on a focal plane of the objective lens.

24. The optical apparatus of claim 17, wherein one of or both of the first and second interferometers are Fabry-Perot interferometers.

25. The optical apparatus of claim 24, wherein one of or both of the first and second Fabry-Perot interferometers are electro-optical devices containing a medium that exhibits one of a Kerr effect and a Pockel effect.

26. The optical apparatus of claim 17, wherein one of or both of the first and second interferometers are Lummer-Gehrcke interferometers.

27. The optical apparatus of claim 26, wherein one of or both of the Lummer-Gehrcke interferometers are electro-optical devices containing a medium that exhibits one of a Kerr effect and a Pockel effect.

28. The optical apparatus of claim 17, wherein one of or both of the first and second interferometers are interference filters.

29. The optical apparatus of claim 28, wherein one of or both of the first and second interference filters are electro-optical devices containing a medium that exhibits one of a Kerr effect and a Pockel effect.

30. The optical apparatus of claim 17, wherein one of or both of the first and second interferometers are frustrated total interference filters.

31. The optical apparatus of claim 30, wherein one of or both of the first and second frustrated total interference filters are electro-optical devices containing a medium that exhibits one of a Kerr effect and a Pockel effect.