Source: http://www.google.com/patents/US20020176149?dq=6,332,126
Timestamp: 2017-11-20 08:23:06
Document Index: 3075490

Matched Legal Cases: ['Application No. 60', 'Application No. 60', 'Application No. 60', 'Application No. 60', 'Application No. 60', 'Application No. 60']

Patent US20020176149 - Variable optical source - Google Patents
A variable optical source 801 to selectively provide a desired optical output signal in response to a control signal is provided. The optical source includes an optical filter that attenuates a broadband optical input signal or a multi-spectral input signal 802. The optical filter is controllable or...http://www.google.com/patents/US20020176149?utm_source=gb-gplus-sharePatent US20020176149 - Variable optical source
Publication number US20020176149 A1
Application number US 10/115,648
Also published as CA2443664A1, EP1386193A2, WO2002082166A2, WO2002082166A3
Publication number 10115648, 115648, US 2002/0176149 A1, US 2002/176149 A1, US 20020176149 A1, US 20020176149A1, US 2002176149 A1, US 2002176149A1, US-A1-20020176149, US-A1-2002176149, US2002/0176149A1, US2002/176149A1, US20020176149 A1, US20020176149A1, US2002176149 A1, US2002176149A1
Inventors Michael Davis, Alan Kersey, John Moon, James Dunphy, James Sirkis, Joseph Pinto, Paul Szczepanek
Original Assignee Michael Davis, Kersey Alan D., John Moon, James Dunphy, James Sirkis, Joseph Pinto, Paul Szczepanek
Patent Citations (23), Referenced by (33), Classifications (45), Legal Events (3)
Variable optical source
US 20020176149 A1
A variable optical source 801 to selectively provide a desired optical output signal in response to a control signal is provided. The optical source includes an optical filter that attenuates a broadband optical input signal or a multi-spectral input signal 802. The optical filter is controllable or programmable to selectively provide a desired filter function. The optical filter 10 includes a spatial light modulator 36, which may comprise an array of micromirrors 52 that effectively forms a two-dimensional diffraction grating mounted in a retro-reflecting configuration. The input optical signal is dispersed onto the array of micro-mirrors 52 along a spectral axis or direction 55 such that input light is spread over a plurality of micromirrors to effectively pixelate the light. The broadband light or signals of the multi-spectral input light is selectively attenuated by flipping or tilting a selected number of micromirrors to thereby deflect a portion of the incident radiation away from the return optical path. The micro-mirrors operate in a digital manner by flipping between a first and second position in response to a control signal 56 provided by a controller 58 in accordance with an attenuation algorithm and an input command 60.
1. A variable optical source, comprising:
a light dispersive element which receives an optical input signal having various wavelength channels of light, which provides a separated light signal having said wavelength channels spatially distributed by a predetermined amount;
a pixellating device, which receives said separated light, having a two dimensional array of pixels, each of said channels being incident on a plurality of pixels, each of said pixels having a first reflection state and a second reflection state in response to a pixel control signal, and said pixellating device providing a reflected separated light signal indicative of light provided from said first reflection state;
a light combining element, which receives said reflected separated light, recombines said reflected separated light, and provides an optical filter output signal indicative of a spectrally filtered optical input signal based on a filter function; and
a controller which generates said pixel control signal indicative of said filter function and wherein said filter function is selectable based on a desired spectral filter profile.
2. The apparatus of claim 1 wherein said pixelating device comprises a micro-mirror device and said pixels comprise micromirrors.
8. The apparatus of claim 1, wherein the light dispersive element disperses the optical channels of the input light onto the pixellating device to substantially separate the optical channels on the pixellating device.
9. The apparatus of claim 1, wherein the light dispersive element disperses the optical channels of the input light onto the pixellating device to substantially overlap the optical channels on the pixellating device.
10. The apparatus of claim 1, wherein the cross-sectional area of at least one channel of said separated input light is generally circular in shape.
11. The apparatus of claim 1, wherein the cross-sectional area of at least one channel of said separated input light is generally elliptical in shape.
12. The apparatus of claim 1, wherein at least one optical channel of said input light is projected onto at least 50 micro-mirrors of said pixellating device.
13. The apparatus of claim 1, wherein micro-mirrors discretely switch from said first position to said second position.
14. A variable optical source, comprising:
a prism element, which receives said separated light having an incidence angle, and which provides a first stabilized light signal;
a pixellating device, which receives said first stabilized light, having a two dimensional array of pixels, each of said channels being incident on a plurality of said pixels, each of said pixels having a first reflection state and a second reflection state in response to a pixel control signal, and said pixellating device providing a reflected separated light signal indicative of light provided from said first reflection state to said prism element;
said prism element providing a second stabilized light signal in response to said reflected separated light signal, said second stabilized light being substantially independent of changes in said incidence angle of said separated light; and
a light combining element, which receives said second stabilized light signal, recombines said second stabilized light signal, and provides an optical filter output signal indicative of a spectrally filtered optical input signal based on a filter function.
15. The apparatus of claim 1 wherein said pixelating device comprises a micro-mirror device and said pixels comprise micromirrors.
16. The apparatus of claim 1 wherein said filter function is: a band pass filter, a low pass filter, a band reject filter, or a high pass filter.
17. The apparatus of claim 1 wherein said filter function is a predetermined optical loss function.
18. The apparatus of claim 1 wherein said output signal has a substantially flat spectral profile.
19. The apparatus of claim 1 wherein said filter function changes dynamically over a predetermined time period.
20. The apparatus of claim 1 wherein said filter function changes continuously based on a predetermined filter change profile.
21. The apparatus of claim 1, wherein the light dispersive element comprises a diffraction grating.
22. The apparatus of claim 1, wherein the light dispersive element disperses the optical channels of the input light onto the pixellating device to substantially separate the optical channels on the pixellating device.
23. The apparatus of claim 1, wherein the light dispersive element disperses the optical channels of the input light onto the pixellating device to substantially overlap the optical channels on the pixellating device.
24. The apparatus of claim 1, wherein the cross-sectional area of at least one channel of said separated input light is generally circular in shape.
25. The apparatus of claim 1, wherein the cross-sectional area of at least one channel of said separated input light is generally elliptical in shape.
26. The apparatus of claim 1, wherein at least one optical channel of said input light is projected onto at least 50 micro-mirrors of said pixellating device.
27. The apparatus of claim 1, wherein micro-mirrors discretely switch from said first position to said second position.
28. A variable optical source, comprising:
an optical lens, located a predetermined lens distance from said dispersive element and having a lens focal length, which receives said separated light, and which provides a focussed light signal;
a pixellating device, which receives said focussed light, having a two dimensional array of pixels, each of said channels being incident on a plurality of said pixels, each of said pixels having a first reflection state and a second reflection state in response to a pixel control signal, and said pixellating device providing a reflected separated light signal indicative of light provided from said first reflection state to said prism element;
a light combining element, which receives said reflected separated light signal, recombines said reflected separated light signal, and provides an optical filter output signal indicative of a spectrally filtered optical input signal based on a filter function; and
said lens distance being different from said focal length so as to provide a substantially constant optical loss over a predetermined wavelength range.
29. The apparatus of claim 1 wherein said pixelating device comprises a micro-mirror device and said pixels comprise micromirrors.
30. The apparatus of claim 1 wherein said lens distance is greater than said focal length.
31. The apparatus of claim 1 wherein said lens distance is less than said focal length.
32. The apparatus of claim 1 wherein said filter function is: a band pass filter, a low pass filter, a band reject filter, or a high pass filter.
33. The apparatus of claim 1 wherein said output signal has a substantially flat spectral profile.
34. The apparatus of claim 1 wherein said filter function changes dynamically over a predetermined time period.
35. The apparatus of claim 1 wherein said filter function changes continuously based on a predetermined filter change profile.
36. The apparatus of claim 1, wherein the light dispersive element comprises a diffraction grating.
37. The apparatus of claim 1, wherein the light dispersive element disperses the optical channels of the input light onto the pixellating device to substantially separate the optical channels on the pixellating device.
38. The apparatus of claim 1, wherein the light dispersive element disperses the optical channels of the input light onto the pixellating device to substantially overlap the optical channels on the pixellating device.
39. The apparatus of claim 1, wherein the cross-sectional area of at least one channel of said separated input light is generally circular in shape.
40. The apparatus of claim 1, wherein the cross-sectional area of at least one channel of said separated input light is generally elliptical in shape.
41. The apparatus of claim 1, wherein at least one optical channel of said input light is projected onto at least 50 micro-mirrors of said pixellating device.
42. The apparatus of claim 1, wherein micro-mirrors discretely switch from said first position to said second position.
43. A variable optical source, comprising:
said light dispersive element dispersing the optical channels of the input light onto said pixelating device to substantially overlap the optical channels on said pixellating device; and
a light combining element, which receives said reflected separated light, recombines said reflected separated light, and provides an optical filter output signal indicative of a spectrally filtered optical input signal based on a filter function.
44. The apparatus of claim 1 wherein said pixelating device comprises a micro-mirror device and said pixels comprise micromirrors.
45. The apparatus of claim 1 wherein said filter function is: a band pass filter, a low pass filter, a band reject filter, or a high pass filter.
46. The apparatus of claim 1 wherein said filter function is a predetermined optical loss function.
47. The apparatus of claim 1 wherein said output signal has a substantially flat spectral profile.
48. The apparatus of claim 1 wherein said filter function changes dynamically over a predetermined time period.
49. The apparatus of claim 1 wherein said filter function changes continuously based on a predetermined filter change profile.
50. The apparatus of claim 1, wherein the light dispersive element comprises a diffraction grating.
51. The apparatus of claim 1, wherein the cross-sectional area of at least one channel of said separated input light is generally circular in shape.
52. The apparatus of claim 1, wherein the cross-sectional area of at least one channel of said separated input light is generally elliptical in shape.
53. The apparatus of claim 1, wherein at least one optical channel of said input light is projected onto at least 50 micro-mirrors of said pixellating device.
54. The apparatus of claim 1, wherein micro-mirrors discretely switch from said first position to said second position.
55. A variable optical source, comprising:
wherein said pixellating device is oriented such that the optical path length for a given wavelength channel is substantially constant across the projected image on the pixellating device.
56. The apparatus of claim 1 wherein said pixelating device comprises a micro-mirror device and said pixels comprise micromirrors.
57. The apparatus of claim 1 wherein said reflected separated light from said first reflection state reflects light substantially perpendicular to a spectral axis along said pixellating device.
58. The apparatus of claim 1 wherein said filter function is: a band pass filter, a low pass filter, a band reject filter, or a high pass filter.
59. The apparatus of claim 1 wherein said filter function is a predetermined optical loss function.
60. The apparatus of claim 1 wherein said output signal has a substantially flat spectral profile.
61. The apparatus of claim 1 wherein said filter function changes dynamically over a predetermined time period.
62. The apparatus of claim 1 wherein said filter function changes continuously based on a predetermined filter change profile.
63. The apparatus of claim 1, wherein the light dispersive element comprises a diffraction grating.
64. The apparatus of claim 1, wherein the light dispersive element disperses the optical channels of the input light onto the pixellating device to substantially separate the optical channels on the pixellating device.
65. The apparatus of claim 1, wherein the light dispersive element disperses the optical channels of the input light onto the pixellating device to substantially overlap the optical channels on the pixellating device.
66. The apparatus of claim 1, wherein the cross-sectional area of at least one channel of said separated input light is generally circular in shape.
67. The apparatus of claim 1, wherein the cross-sectional area of at least one channel of said separated input light is generally elliptical in shape.
68. The apparatus of claim 1, wherein at least one optical channel of said input light is projected onto at least 50 micro-mirrors of said pixellating device.
69. The apparatus of claim 1, wherein micro-mirrors discretely switch from said first position to said second position.
This application claims the benefit of U.S. Provisional Application No. 60/281,079, filed Apr. 3, 2001; U.S. Provisional Application No. 60/311,002, filed Aug. 8, 2001; U.S. Provisional Application No. 60/365,682, filed Mar. 18, 2002; U.S. Provisional Application No. 60/365,446, filed Mar. 18, 2002; U.S. Provisional Application No. 60/365,741, filed Mar. 18, 2002; and U.S. Provisional Application No. 60/365,461, filed Mar. 18, 2002, all of which are incorporated herein by reference in their entirety.
The present invention relates to optical sources, and more particularly to variable optical sources including a spatial light modulator, such as an array of micro-mirrors to selectively shape or attenuate a broadband or channelized optical input signal to provide a desire optical output signal.
It is known in the field of electronics to provide a variable electronic power supply or source for generating an electrical signal having a desired signal profile. These variable electronic source are uses in a number of test and measurement applications such as trouble shooting systems, measuring operational parameters of a system, and developing new products.
In the field of optics a comparable variable optical source is desirable for the same reasons stated above. Currently, optical sources for test and measurement application comprise a laser or plurality of lasers that may be individually tuned to provide the desired optical output signal, which is expensive and time-consuming to generate the desire output signal. It is therefore desirable to provide a variable optical source that can easily and inexpensively provide a desired optical output signal using a broadband optical source and/or a multi-spectral optical source.
An object of the present invention is to provide a variable optical source having a spatial light modulator, wherein the spatial light modulator pixelates the spectrum of the optical signal, to thereby permit shaping or attenuating a broadband or channelized optical input signal for providing a desired output signal.
In accordance with an embodiment of the present invention, a variable optical source, includes a light dispersive element which receives an optical input signal having various wavelength channels of light, which provides a separated light signal having said wavelength channels spatially distributed by a predetermined amount; a pixellating device, which receives said separated light, having a two dimensional array of pixels, each of said channels being incident on a plurality of pixels, each of said pixels having a first reflection state and a second reflection state in response to a pixel control signal, and said pixellating device providing a reflected separated light signal indicative of light provided from said first reflection state; a light combining element, which receives said reflected separated light, recombines said reflected separated light, and provides an optical filter output signal indicative of a spectrally filtered optical input signal based on a filter function; and a controller which generates said pixel control signal indicative of said filter function and wherein said filter function is selectable based on a desired spectral filter profile.
[0007]FIG. 1 is a block diagram of an optical filter including a spatial light modulator in accordance with the present invention;
[0008]FIG. 2 is a block diagram of a spatial light modulator of the optical filter of FIG. 1 having a micro-mirror device, wherein the optical channels of a WDM input light are substantially dispersed onto the micro-mirror device, in accordance with the present invention;
[0009]FIG. 3 shows a pictorial view of a partial row of micro-mirrors of the micro-mirror device of FIG. 2 in accordance with the present invention;
[0010]FIG. 4 is a plan view of a micro-mirror of the micro-mirror device of FIG. 2 in accordance with the present invention;
[0011]FIG. 5 is a plot of an input optical signal having 50 GHz spacing;
[0012]FIG. 6 is a plot of the power of the optical channels imaged onto the micro-mirror device, wherein the optical channels of a WDM input light are substantially dispersed onto the micro-mirror device as shown in FIG. 2, in accordance with the present invention;
[0013]FIG. 7 is a graphical representation of a transmission filter function of an optical filter, wherein the optical channels of a WDM input light are substantially dispersed onto the micro-mirror device as shown in FIG. 2, in accordance with the present invention;
[0014]FIG. 8 is a plot of attenuation curve when a single channel is dropped from the optical input signal of the optical filter of FIG. 2;
[0015]FIGS. 9a-c are block diagrams of a spatial light modulator of another embodiment of an optical filter having a micro-mirror device, wherein the optical channels of a WDM input light are overlappingly dispersed onto the micro-mirror device in various degrees of overlap, in accordance with the present invention;
[0016]FIG. 10 is an expanded pictorial representation of an illuminated portion of the micro-mirror device of FIG. 9a, that shows the intensity distribution for three overlapping optical channels of the WDM input light, in accordance with the present invention;
[0017]FIG. 11 is a graphical representation of a transmission filter function of an optical filter, wherein the optical channels of a WDM input light are overlappingly dispersed onto the micro-mirror device as shown in FIG. 6, in accordance with the present invention;
[0018]FIG. 12a is a block diagram of the spectral plane in partial illustration of another embodiment of an optical filter including a spatial light modulator in accordance with the present invention;
[0019]FIG. 12b is a block diagram of the spatial plane of the embodiment of the optical filter of FIG. 9a;
[0020]FIG. 13 is a block diagram of a closed-loop DGEF system in accordance with the present invention;
[0021]FIG. 14 is a perspective view of a portion of a known micro-mirror device;
[0022]FIG. 15 is a plan view of a micro-mirror of the micro-mirror device of FIG. 14;
[0023]FIG. 16 is a pictorial cross-sectional view of the micro-mirror device of the spatial light modulator of FIG. 14 disposed at a predetermined angle in accordance with the present invention;
[0024]FIG. 17 is a pictorial cross-sectional view of the micro-mirror device of the spatial light modulator of FIG. 14 disposed at a predetermined angle in accordance with the present invention;
[0025]FIG. 18 is a graphical representation of the micro-mirror device of FIG. 17 in accordance with the present invention;
[0026]FIG. 19a is a graphical representation of a portion of the optical filter wherein the grating order causes the shorter wavelengths of light to image onto the micromirror device that is closer than the section illuminated by the longer wavelengths, in accordance with the present invention;
[0027]FIG. 19b is a graphical representation of a portion of the optical filter wherein the grating order causes the longer wavelengths of light to image onto the micromirror device that is closer than the section illuminated by the shorter wavelengths, in accordance with the present invention;
[0028]FIG. 20 is a block diagram of another embodiment of an optical filter including a spatial light modulator in accordance with the present invention;
[0029]FIG. 21 is a block diagram of the micro-mirror device of FIG. 14 having a micro-mirror device, wherein the optical channels of a WDM input light are substantially dispersed onto the micro-mirror device, in accordance with the present invention;
[0030]FIG. 22 is a plot showing the commanded gain profile and the resulting gain profile of an optical filter in accordance with the present invention;
[0031]FIG. 23 is a plot showing the error the commanded gain profile and the resulting gain profile of an optical filter of FIG. 22;
[0032]FIG. 24 is a plot showing the commanded gain profile and the resulting gain profile of an optical filter in accordance with the present invention;
[0033]FIG. 25 is a plot showing the error the commanded gain profile and the resulting gain profile of an optical filter of FIG. 24;
[0034]FIG. 26 is a plot showing a WDM input signal having a plurality of unequalized optical channels provided to a closed-loop DGEF system in accordance with the present invention;
[0035]FIG. 27 is a plot showing the equalized output signal of the closed-loop DGEF system having an input signal shown in FIG. 26;
[0036]FIG. 28 is a graphical representation of the light of an optical channel reflecting off a spatial light modulator, wherein the light is focused relatively tight, in accordance with the present invention;
[0037]FIG. 29 is a graphical representation of the light of an optical channel reflecting off a spatial light modulator, wherein the light is focused relatively loose compared to that shown in FIG. 28, in accordance with the present invention;
[0038]FIG. 30 is a block diagram of another embodiment of an optical filter including a spatial light modulator in accordance with the present invention;
[0039]FIG. 31 is an elemental illustration of the optical filter of FIG. 1 in accordance with the present invention;
[0040]FIG. 32 is a perspective illustration of an embodiment of an optical filter in accordance with the present invention;
[0041]FIG. 33 is an alternative perspective view of the optical filter of FIG. 32;
[0042]FIG. 34 is a perspective illustration of an embodiment of a beam generation module (BGM) in accordance with the present invention;
[0043]FIG. 35 is an alternative perspective view of the beam generation module of FIG. 34;
[0044]FIG. 36 is a perspective illustration of an embodiment of a curved mirror mount in accordance with the present invention;
[0045]FIG. 37 is a perspective illustration of an embodiment of a diffraction grating mount in accordance with the present invention;
[0046]FIG. 38 is an alternative perspective view of the diffraction grating mount of FIG. 37;
[0047]FIG. 39 is a perspective illustration of an embodiment of a turning mirror mount in accordance with the present invention;
[0048]FIG. 40 is a perspective illustration of an embodiment of an optical filter including a DMD chip and board assembly in accordance with the present invention;
[0049]FIG. 41 is an alternative perspective view of the optical filter of FIG. 37;
[0050]FIG. 42 is a perspective view of the optical components of another embodiment of an optical filter embodying the present invention;
[0051]FIG. 43 is a simplified side elevation view of a collimating lens and spatial light modulator of an optical filter, in accordance with the present invention;
[0052]FIG. 44 is a simplified side elevation view of a collimating lens and spatial light modulator assembly of an optical filter, in accordance with the present invention;
[0053]FIG. 45 is a perspective view of the chisel prism of the optical filter of FIG. 42;
[0054]FIG. 46 is a top plan view of the optical channel filter of FIG. 39;
[0055]FIG. 47 is side elevational view of a portion of the optical channel filter of FIG. 46;
[0056]FIG. 48 is an illustration of the optical channel layout on the micromirror device in accordance with the present invention;
[0057]FIG. 49 is a plot of the intensity of the optical channels taken across the micromirror device of FIG. 46 along line 46-46;
[0058]FIG. 50 is a graphical representation of the retro-reflection of the input light when the micro-mirrors flip about an axis perpendicular to the spectral axis;
[0059]FIG. 51 is a graphical representation of the retro-reflection of the input light when the micro-mirrors flip about an axis parallel to the spectral axis;
[0060]FIG. 52 is a plot comparing the power loss of the retro-reflected input signal versus wavelength, when the micromirrors flip about the axis parallel to the spectral axis and when the micro-mirrors flip about the axis perdendicular to the spectral axis;
[0061]FIG. 53 is a plot comparing the power loss of the retro-reflected input signal versus wavelength, when the micromirrors flip about the axis parallel to the spectral axis and when the micro-mirrors flip about the axis perdendicular to the spectral axis;
[0062]FIG. 54 is a perspective view an optical filter device similar to that shown in FIG. 42 in accordance with the present invention;
[0063]FIG. 55 is a perspective view of the optical chassis of the optical filter of FIG. 54;
[0064]FIG. 56 is a perspective view of the Fourier lens and mount of the optical filter of FIG. 54;
[0065]FIG. 57 is an exploded view perspective view of Fourier lens and mount of the optical filter of FIG. 54;
[0066]FIG. 58 is perspective view of a portion of the optical filter of FIG. 54;
[0067]FIG. 59 is an exploded perspective view of a grating mount of the optical filter of FIG. 54;
[0068]FIG. 60 is an exploded perspective view of the grating mount of FIG. 59;
[0069]FIG. 61 is a perspective view of a telescope of the optical filter of FIG. 47;
[0070]FIG. 62 is an exploded perspective view of the telescope of FIG. 54;
[0071]FIG. 63 is a perspective view of a collimating lens of FIG. 54;
[0072]FIG. 64 is a block diagram of a spatial light modulator of an optical filter that includes a plurality of optical filters, wherein the optical channels are distinctly projected onto the micromirror device, in accordance with the present invention.
[0073]FIG. 65 is a block diagram of an embodiment of the optical filter functioning as a dynamic gain equalization filter in accordance with the present invention;
[0074]FIG. 66 is a block diagram of an embodiment of the optical filter functioning as a drop filter in accordance with the present invention;
[0075]FIG. 67 is a block diagram of an embodiment of the optical filter functioning as an optical spectral analyzer in accordance with the present invention;
[0076]FIG. 68 is a block diagram of an embodiment of the optical filter functioning as a reconfigurable optical add/drop multiplexer in accordance with the present invention;
[0077]FIG. 69 is a block diagram of an embodiment of the optical filter functioning as an optical deinterleaver/interleaver device in accordance with the present invention;
[0078]FIG. 70 is a block diagram of an embodiment of the optical filter functioning as a variable optical filter in accordance with the present invention;
[0079]FIG. 71 is a block diagram of an embodiment of the optical filter functioning as a variable optical filter in accordance with the present invention;
[0080]FIG. 72 is a block diagram of an embodiment of the optical filter functioning as a variable optical filter in accordance with the present invention;
[0081]FIG. 73 is a block diagram of a variable optical source in accordance with the present invention;
[0082]FIG. 74 is a block diagram of a test set-up for determining the cross-talk of a device under test including a variable optical source in accordance with the present invention;
[0083]FIG. 75 is a block diagram of a test set-up for measuring the dynamic range of a device under test including a variable optical source in accordance with the present invention;
[0084]FIG. 76 is a block diagram of a test set-up for determining the immunity to broadband noise of a device under test including a variable optical source in accordance with the present invention; and
[0085]FIG. 77 is a block diagram of the electronics of the DGEF of FIG. 54 in accordance with the present invention.
As shown in FIGS. 1 and 2, an optical filter, generally shown as 10, selectively attenuates or filters a wavelength band(s) of light (i.e., optical channel(s)) or a group(s) of wavelength bands of an optical WDM input signal 12 in response to a control signal. Each of the optical channels 14 (see FIG. 2) of the input signal 12 is centered at a respective channel wavelength (λ1,λ2,λ3, . . . λN) The optical filter is controllable or programmable to selectively provide a desired filter function, which will be described in greater detail hereinafter. The control signal may be provided directly by a user from a control panel or by a processor that is programmed to provide a control signal of a desired output signal. The capability of selectively varying the filter function enables the optical filter to operate as a variable optical source, as shown in FIGS. 73-76.
In FIG. 73, an optical source 800 provides a broadband input signal to the input of an optical filter 10 similar to that shown in FIGS. 1, 2 and 9 a to provide a variable optical source 801. As will be described in greater detail hereinafter, the input signal 802 is spread spectrally over a spatial light modulator 36 comprising a plurality of micromirrors 52 of a micromirror device 50 to effectively pixelate the input signal. The micromirrors are then flipped between a first and second position to provide the desire input light to the output fiber or reflect a portion of the light away from the output fiber to selectively attenuate the input signal.
A variety of broadband sources 800 can be used ranging from the ASE of a pumped Er+ system to an LED. In addition, due to the flexibility of the spatial light modulator 36, wavelengths ranging from the visible to the infrared can be used with appropriate devices. The broadband source is intended to provide light covering the entire range of interest, permitting the optical filter 10 the maximum flexibility in producing variable optical outputs.
As shown in FIG. 73, the spatial light modulator 36 of the optical filter 10 may be controlled by a control signal 60 or internally programmed to provide a variety of optical filter functions to produce a corresponding number of spectral source profiles or output signals. For instance, the micromirrors 50 of the spatial light modulator 36 may be flipped to provide a full broadband source at 804, possibly altered to flatten and provide uniform illumination, or other shapes such as a Gaussian shape. Second, the optical filter may be configured to output a subset of the broadband input, exploiting the variable passband features of the micromirror device 50. Third, the optical filter may be configured to output a narrow bandwidth optical signal, which can be static or scanned over the spectral region of interest. Third, the optical filter may be configured to output multi-spectral components, which may be equally spaced set of signals to form a comb, or different arbitrary located signals.
It will be appreciated that the variable optical source is useful for testing of optical networks and components. By providing such a flexible solution, parameters such as wavelength dependence, dynamic range, optical noise floor dependence, optical crosstalk and many others can be tested using a source such as the one described here.
While the optical variable source has been described as having a broadband input source, the present invention contemplates a input source that provides a multi-spectral (or channelized) input source as shown in FIGS. 74-76. Such a variable optical source is useful in various sectors of the test and measurement field such as installation and maintenance of equipment, manufacturing test, and research and development. Throughout each of these sectors similar type of tests may be run for various purposes, ranging from an initial installation of a network to the development work for a next generation system. Some of these tests include cross-talk testing, broadband noise immunity test, and dynamic range testing.
In FIG., 74, for example, a test set-up using the variable optical filter 10 for testing for crosstalk sensitivity in a device under test (DUT) 810 is shown. The ability of the optical filter 10 of the variable source 801 to precisely attenuate or block one or more channels in a DWDM system, which will be described in greater detail hereinafter, permits the testing of systems or components. The optical filter 10, in response to a control signal 60, selectively attenuates and blocks the input channels 14 of the multi-spectral input to provide an output signal 812 that includes a primary signal and one or more secondary crosstalk test signals. When the output signal is injected into the device under test 810 (DUT) the effects of the crosstalk signals can be evaluated. Each of the primary and secondary signal powers and wavelengths can be adjusted to permit complete characterization of the DUT.
In FIG. 75, a test set-up using the variable optical filter 10 for testing the dynamic range of a DUT 810. One important characteristic of some optical test equipment (the DUT) is its ability to resolve both a weak and strong optical signals in close proximity to each other. This specification typically should remain constant of their entire wavelength range of the device. The optical filter functions similarly as that described hereinbefore in FIG. 74. The optical filter 10, in response to a control signal 60, selectively attenuates and blocks the input channels 14 of the multi-spectral input 802 to provide an output signal 812 that includes a primary signal and a small adjacent signal.
In FIG. 76, a test set-up using the variable optical filter 10 for testing for broadband noise immunity of a system or optical component (i.e., DUT). The variable optical source 801 can test a DUT's susceptibility to background noise present in the incoming optical signal. The variable source can test these characteristics in a DUT 810 with the flexibility of incrementing the level and bandwidth of the background noise signal versus the primary optical channel.
To accomplish this flexibility, an optical coupler or combiner 812 combines a broadband signal and a primary signal together and provides this combined signal to the optical filter 10. Similar to that described hereinbefore the optical filter selectively attenuates the combined input signal to adjust the strength as well as the spectral content of the broadband signal. Alternatively, the optical filter 10 may first attenuated the broadband signal and then the Primary Signal is combined with the output signal of the optical filter before being provided to the DUT.
While the variable source 801 may selectively provide a number of test or output signals for performing a number of different tests, as described hereinbefore, the present invention is not limited to these embodiments or tests and contemplates the selectability of any desired filter function to provide any desired output signal. Further, one will appreciated that any input signal 802 may be provided to the optical filter 10 to generated the desired output signal.
The following is a detailed description of the optical filter 10. To simply the description of the optical filter 10 embodying the present invention, the following description of the optical filter will be described as a DGEF. However, as discussed hereinbefore, the optical filter may be programmed or controlled to have any desired filter function to provide any desire output signal.
As shown in FIG. 2, the spatial light modulator 36 comprises a micro-mirror device 50 having a two-dimensional array of micro-mirrors 52, which cover a surface of the micro-mirror device. The micro-mirrors 52 are generally square and typically 14-20 μm wide are spaced approximately 1 μm. FIG. 3 illustrates a partial row of micro-mirrors 52 of the micro-mirror device 50. The micro-mirrors may operate in a “digital” manner. In other words, the micro-mirrors either lie flat in a first position and thus reflect light back along the return path, as indicated by arrows 53. Or the micro-mirrors 52 can be tilted, flipped or rotated to a second position such that the micro-mirrors direct light out of or away from the return path at the predetermined angle (e.g., 20 degrees), as indicated by arrows 56. As described herein the positions of the mirrors, either flat or tilted, are described relative to the optical path wherein “flat” refers to the mirror surface positioned orthogonal to the light path, either coplanar in the first position or parallel as will be more fully described herein after. The micro-mirrors 52 flip about an axis 51 perpendicular to the spectral axis 55, as shown in FIG. 4. One will appreciate, however, that the micro-mirrors may flip about any axis, such as perpendicular to the spatial axis 57 or at a 45 degree angle to the spatial axis (i.e., flip about a diagonal axis extending from opposing corners of the micromirrors).
As best shown in FIGS. 1-3, the micro-mirror device 50 is oriented to reflect the focused light back through the bulk lens 34 to the pigtail 22, as indicated by arrows 53, when the micro-mirrors 52 are disposed in the first position, and reflects the focused light away from the bulk lens 34 when the micro-mirrors 52 are disposed in the second position, as indicated by arrows 56. This “digital” mode of operation of the micro-mirrors advantageously eliminates the need for any type of feedback control for each of the micro-mirrors. The micro-mirrors are either “on” or “off” (i.e., first position or second position, respectively), and therefore, can be controlled by simple digital logic circuits.
[0109]FIG. 2 further illustrates the outline of the optical channels 14 of the optical input signal 12, which are dispersed off the diffraction gratings 30 and focused by lens 34, onto the array of micro-mirrors 52 of the micro-mirror device 50. The optical channels have an elliptical cross-section to project the beam over a predetermined number of micro-mirrors 52.
As shown in FIGS. 2 and 6, the optical channels 14 are dispersed and have an elliptical cross-section, such that the optical channels do not substantially overlap spectrally when focused onto the spatial light modulator 36. For example, as shown in FIG. 6, the optical channels 14 are sufficiently separated such that when a channel is substantially attenuated or dropped (e.g. approximately 30 dB power loss) the adjacent channels are attenuated less than approximately 0.1% for unmodulated signals and less than approximately 0.2% for a modulated signal. In other words, as shown in FIG. 7 and 8, the optical channels are substantially separated and non-overlapping when an optical channel is attenuated or dropped (PLoss) such that the power of the adjacent channel drops less than a predetermined level (δA) at a predetermined delta (Δf) from the center frequency (or wavelength) of the adjacent channels. For example, for a 50 GHz WDM input signal wherein an optical channel at λ2 is attenuated (PLoss) greater than 30dB, the loss (δA) at adjacent channels is approximately less than 0.2dB at the channel center +/−10 GHz.
[0115]FIG. 7 is representative of an optical filter function 70 of the optical filter 10, wherein a number of the micro-mirrors 52 illuminated by the optical channel 14 at λ2 are tilted away 56 from the return path, and the micro-mirrors of the other optical channels at wavelengths at λ1, λ3, −λN are flat (i.e., first position) to reflect the light back along the return path 53. Effectively, the optical channel 14 at λ2 is dropped from the input light 12. As described hereinabove, the attenuation of the optical channel at λ2 may be adjusted by tilting a predetermined number of micro-mirrors to drop a corresponding amount of light to achieve the desired level of loss.
In FIGS. 9a-c, another embodiment of an optical filter is shown, which is similar to the optical filter 10 shown in FIGS. 1-3, except the diffraction grating 30 disperses the optical channels 14 of the input light 12 onto the micro-mirror device 50, such that the optical channels are not substantially separated, as defined hereinbefore, but overlapped, and have a generally circular cross-section. FIG. 9a shows an embodiment wherein the optics (i.e., collimating lens 26 and bulk lens 34) spread or disperse the input light onto the micromirror device such that the optical channels substantially overlap. FIGS. 9b and 9 c show embodiments with varying degrees of overlap of the optical channels imaged onto the micromirror device. While present invention describes the optical channels having a generally circular cross-section, one will appreciate the cross-section may be elliptical or other geometric shape.
[0118]FIG. 10 shows the intensity distribution for three 50-GHz separated optical ITU channels of FIG. 9. The position in the spectral domain of the attenuation is determined by actuating micro-mirrors 52 in a specific spectral region of the device along the spectral direction 55. Variable attenuation in a given spectral band is achieved by actuating micro-mirrors primarily along the spatial direction 57 at the preselected spectral position. As described hereinbefore, the number of micro-mirrors 52 that are tilted determines the attenuation of the optical channel 14 or spectral band. One will note, however, that some of the micro-mirrors reflect light of more than one optical channel or band, and therefore when such a micro-mirror is tilted away from the return path, each corresponding optical channel is attenuated by a predetermined amount. Consequently, if, for example, a substantial number of the micro-mirrors 52 illuminated by the optical channel 14 at λ2 are titled away from the return path, not only will the optical channel at λ2 be fully attenuated, but also a substantial portion of the adjacent optical channels (i.e., at λ1, λ3) will be attenuated, as shown in FIG. 11. FIG. 11 shows the optical filter function 76 of the optical filter of FIG. 9, wherein a substantial number of the micro-mirrors 52 that are illuminated by the optical channel at λ2 are tilted away from the return path. Advantageously, the overlapping of the optical channels 14 on the micro-mirror device 50 provides for a smooth attenuation transition between optical channels or bands.
In another exemplary embodiment, a DGEF 80 is provided in FIGS. 12a and 12 b that is substantially similar to the DGEF 10 of FIGS. 1 and 2, and therefore, common components have the same reference numeral. The DGEF 80 replaces the circulator 28 of FIG. 1 with a second pigtail 82. The pigtail 82 has a glass capillary tube 84 attached to one end of the pigtail. The pigtail 82 receives the optical channels reflected from the micro-mirror device 50 (FIG. 10) back along a return optical path 53. Note that in FIG. 12a pigtails 82 and 24 in one embodiment (in reality) are coplanar in the top view and are shown as separate in the view for illustration purposes. Specifically, pigtail 82 receives the compensated optical channels 14 (FIG. 10) reflected back along the return optical path 53, which are reflected back from the spatial light modulator 36. Lens 34 of the embodiment shown is a cylindrical lens to separate the source path 32 and the return path 55 and thereby accommodates the separate source and receive pigtails 27,82. In another embodiment the pigtail 22, the light dispersive element 30 and/or the spatial light modulator 36 are tilted or positioned to offset the reflected path 53 such that the reflected light is focused on the second pigtail 82. The true separation of the source path 28, 32 and the return path 53 is best shown in FIG. 12b.
Referring to FIG. 13, a closed-loop system 90 is provided wherein an input signal 12 is provided to the DGEF 10, which selectively attenuates the optical channels 14 or wavelength bands to equalize the power of the input signal over a desired spectrum, and outputs an equalized output signal 38 at an optical fiber 91. An optical coupler 92 taps off a portion of the equalized output signal 38 of the DGEF 10 to an optical channel monitor (OCM) or optical signal analyzer (OSA) 94. The channel monitor 94 provides a sense signal 95, which is indicative of at least the power or gain of each optical channel 14 or wavelength band. In response to the sense signal 95, a processor 96 generates and provides the control signal 60 to controller/interface board 58 which in turn commands the micro-mirror device 50 (see FIG. 2) to flip the appropriate micro-mirrors 52 to attenuate (e.g. flatten or equalize) the input signal 12, as will be described in greater detail hereinafter.
The micro-mirror device 50 of FIGS. 1 and 2 may be similar to the Digital Micromirror Device™ (DMD™) manufactured by Texas Instruments and described in the white paper entitled “Digital Light Processing™ for High-Brightness, High-Resolution Applications”, white paper entitled “Lifetime Estimates and Unique Failure Mechanisms of the Digital Micromirror Device (DMD)”, and news release dated September 1994 entitled “Digital Micromirror Display Delivering On Promises of ‘Brighter’ Future for Imaging Applications”, which are incorporated herein by reference.
[0122]FIG. 14 illustrates a pair of micro-mirrors 52 of such a micromirror device 100 manufactured by Texas Instruments, namely a digital micromirror device (DMD™). The micromirror device 100 is monolithically fabricated by CMOS-like processes over a CMOS memory 102. Each micro-mirror 52 includes an aluminum mirror 104, approximately 16 μm square, that can reflect light in one of two directions, depending on the state of the underlying memory cell 102. Rotation, flipping or tilting of the mirror 104 is accomplished through electrostatic attraction produced by voltage differences between the mirror and the underlying memory cell. With the memory cell 102 in the on (1) state, the mirror 104 rotates or tilts approximately +10 degrees. With the memory cell in the off (0) state, the mirror tilts approximately −10 degrees. As shown in FIGS. 14 and 15, the micro-mirrors 72 flip about an axis 105.
[0123]FIG. 16 illustrates the orientation of a micro-mirror device 100 similar to that shown in FIG. 14, wherein neither the on or off state of the micro-mirrors 52 is parallel to the base or substrate 110, as shown in FIG. 3. Consequently, the base 110 of the micro-mirror device 100 is mounted at a non-orthogonal angle α relative to the collimated light 32 (see FIG. 1) to position the micro-mirrors 52, which are disposed at the first position, perpendicular to the collimated light, so that the reflected light off the micro-mirrors in the first position reflect substantially back through the return path, as indicated by arrows 53. Consequently, the tilt angle of the mirror between the horizontal position and the first position (e.g., 10 degrees) is approximately equal to the angle α of the micro-mirror device.
In using the micro-mirror array device 100, it is important that the reflection from each micro-mirror 72 adds coherently in the far-field, so the angle a to which the micro-mirror device 100 is tilted has a very strong influence on the overall efficiency of the device. FIG. 17 illustrates the phase condition of the micro-mirrors in both states (i.e., State 1, State 2) for efficient reflection in either condition.
In an exemplary embodiment of the micro-mirror device 100, the effective pixel pitch ρ is about 19.4 μm, so for a mirror tilt angle β of 9.2 degrees, the array is effectively blazed for Littrow operation in the n=+2 order for the position indicated as Mirror State 1 in FIG. 17 (i.e., first position for a wavelength of about 1.55 μm). For Mirror State 2, the incident angle γ on the micro-mirror device 100 is now 9.2 degrees and the exit angle ε from the array is 27.6 degrees. Using these numbers, the micro-mirror device is nearly blazed for fourth-order for mirrors in Mirror State 2.
[0126]FIG. 18 graphically illustrates the micro-mirror device 100 wherein the micro-mirrors 52 are disposed in the retro-reflective operation (i.e., first position), such that the incident light reflects back along the return path 53 (see. FIG. 1). For retro-reflective operation, the micro-mirror device 100 acts as a blazed grating held in a “Littrow” configuration, as shown in FIG. 1, with the mount angle (α) equal to the mirror tilt “β” or blaze angle (e.g., 9.2 degrees). The grating equation (i.e., sinθ1, +sin θm=mλ/d) provides a relationship between the light beam angle of incidence (θ1) angle of reflection, (θm) the pitch (d) of the micro-mirror array; the mirror tilt; and the wavelength of the incident light (λ). Introducing the micro-mirror device 100 at the focal plane 115 implements the critical device feature of providing separately addressable groups of mirrors to reflect different wavelength components of the beam. Because of the above reflection characteristics of the micro-mirror device 100, with the micro-mirror 100 in the focal plane 115, the beam is reflected as from a curved concave (or convexed) mirror surface. Consequently, when the micro-mirror device is oriented to retro-reflect at a wavelength hitting near the mirror center, wavelengths away from the center are reflected toward the beam center (FIG. 1) as if the beam were reflected from a curved concave mirror. In other words, the micro-mirror device 100 reflects the incident light 112 reflecting off the central portion of the array of micro-mirrors directly back along the incident angle of the light, while the incident light 112 reflecting off the micro-mirrors disposed further away from the central portion of the array progressively direct the light inward at increasing angles of reflection, as indicated by arrows 114.
[0127]FIGS. 19a and 19 b illustrate a technique to compensate for this diffraction effect introduced by the micromirror array, described hereinbefore. FIG. 19a illustrates the case where a grating order causes the shorter wavelength light to hit a part of the micromirror array 100 that is closer than the section illuminated by the longer wavelengths. In this case the Fourier lens 34 is placed at a distance “d” from the grating 30 that is shorter than focal length “f” of the Fourier lens. For example, the distance “d” may be approximately 71 mm and the focal length may be approximately 82 mm. It may be advantageous to use this configuration if package size is limited, as this configuration minimizes the overall length of the optical train.
[0128]FIG. 19b illustrates the case where the grating order causes the longer wavelengths to hit a part of the micromirror array 100 that is closer than the section illuminated by the shorter wavelengths. In this case the Fourier lens is placed a distance “d” from the grating 30 that is longer than focal length “f” of the Fourier lens 34. This configuration may be advantageous to minimize the overall area illuminated by the dispersed spectrum on the micromirror array.
Each section is numbered outward from zero with sections to the left of section 0 being positive and the sections to the right of section 0 being negative. The section 0 is at the spatial center of the section pattern. The origin of the entire pattern is the upper left hand corner of section 0. As shown in FIG. 21 for example, section —3 is shown at maximum attenuation step of 12, and section 0 is shown having an attenuation step of 7. All other sections have an attenuation step of zero (0). Sections 3 and 4 are shaded to illustrate the pattern of the sections on the micro-mirror device 100. Optical channels 14 centered at λ1, λ2 substantially reflect a selected section.
The attenuation algorithm receives input indicative of the power of the optical channels 14 or wavelengths over the selected spectrum of the WDM signal. After eliminating channels that are not powered (i.e. the power level is below some predetermined threshold level) the algorithm compares the gain profile of the WDM signal and determines a set of attenuations versus wavelength. The attenuation algorithm takes the set of attenuations versus wavelength {λ15Ai} and turn them into a list of section “Attenuation Step” versus Section Number. The algorithm then commands the micro-mirror device 100 to flip the appropriate micro-mirrors 52.
where I(ρ;λ) is the intensity pattern of the beam on the micro-mirror device 100 for a given wavelength, D(ρ) is the complex spatial pattern of “on” pixels on the micro-mirror device 100, and β=xs{circumflex over (x)}s+ysŷs is the transverse spatial coordinate vector. The function D has constant phase if the micro-mirror device 100 lies in a true Fourier plane (effective focal plane) of the system and optical aberrations and focusing errors are small compared to wavelength.
Due to the diffraction grating 30, the wavelength dependence of I(ρ) can be expressed as I(ρ)=Ix (xs−ρβ)Iy (ys) where Ix and Iy are the beam shapes in the xs and ys direction respectively, and β is a calibration coefficient.
The spatial pattern on the micro-mirror device 100 can be expressed as a sum of spatially distinct sections D  ( ρ ) = ∑ i = 1 N  S  ( x s - γ   λ i )  R  ( y s ; h i ) ( 2 )
where S(xs) is a function of the effective “shape” of the section of the micro-mirror device 100 in the spectral direction (for example they are triangular due to the “diamond” shape of the micro-mirrors 52 when using a suitably oriented DMD device), and R(y) is approximated as a “rectangle” function that is unity for |ys|<h and zero otherwise.
Collecting the above results, one obtains Pc  ( λ ) = ∑ i = 1 N  M  ( λ , λ 1 )  L M  ( h i ) ( 3 )
where the matrix M is essentially the instrument response function convolved with the pixel shape function S. Experimentally, this function is known to be Gaussian to good approximation.
The reflected power off Section j at the peak λj (LM(hj) ) can be calculated with a couple of assumptions. Assuming the beam is spatially separable and the beam has a Gaussian shape in the spatial dimension ys, L M  ( h j ) ≈ 1 - C  [ erf  ( H w y ) - erf  ( H - hj w y ) ] ( 4 )
where hj is the physical height of the “off” pixels for the j'th section on the micro-mirror device 100, H is the physical height of the sections of the micro-mirror device 100, C is called the “spectral overlap”, which is a single semi-empirical parameter which describes the spectral beam shape and pixel shape details, and wy is the Gaussian 1/e HW of the beam in the spatial direction. Note that the “Attenuation Step” AS is related to the parameter AS=w*hj/p, where p is the length of an individual pixel and w is the width (in number of pixels) of the section of the micro-mirror device 100.
Although this model allows one to predict what a filter will look like at a given Attenuation step for a given Section Number, a different problem is usually faced. Typically one is supplied with a set of {λ1, A1}, where A1=10 log10(PC(λC1)) and there is a need to solve for the h vector. Note that the command wavelengths λc1 (which typically lie on the ITU grid)probably don't correspond to sections λi of the micro-mirror device 100.
To do this we use the following procedure. First the matrix M is approximated as a Gaussian. The loss at an arbitrary wavelength can be approximated from Equation (3) as P C  ( λ ) = ∑ j = 1 N  L M  ( h j )  N j  exp  [ - ( λ - λ j w j ) 2 ] ( 5 )
where Nj is a normalization constant. The parameters (center wavelength and width) of each section are determined empirically.
One turns the A (usually in dB) into linear loss vector L. L is sampled onto the set of wavelengths defined by the sections to get Lst={square root}{square root over (Pc(λt))} Equation (5) defines a sparse matrix operator equation that can be inverted using standard techniques to yield the LM solution vector. The Attenuation Step is then found from a look up table of Attenuation Step for a given linear attenuation LMi as calculated from Equation (4).
To mitigate the error introduced by the regularization filter, a second iterative procedure is applied to the resultant h vector to bring the filter values into agreement at the commanded wavelengths. Given the vector h, the resulting attenuation values Lc are calculated at the command wavelengths. The difference between the commanded attenuations L and the calculated attenuations Lc P for the p-th iteration is then “fed back” into a new “command” vector Lc P+1. Note that Lc P=L calculated from the inverse of the filter operator matrix and the regularized input data.
FIGS. 22-25 show data of a DGEF similar to that shown in FIG. 1 having a micro-mirror device 100, as described hereinbefore, whereby the flipping of the micro-mirrors is controlled by the above described gain equalizing algorithm. FIG. 22 compares a desired or commanded filter profile 180, having 10 dB loss at a selected wavelength with the slopes of the function being 2.5 dB/nm, to the actual filter profile 182 provided by the DGEF. FIG. 23 shows the error 184 in dB between the commanded filter profile 180 and the actual filter profile 182 of FIG. 22.
[0155]FIG. 24 compares a commanded filter profile 186, having a more complex function than that shown in FIG. 22, to the actual filter profile 188 provided by the DGEF. FIG. 25 shows the error 190 in dB between the commanded filter profile 186 and the actual filter profile 188 of FIG. 22.
[0156]FIGS. 26 and 27 show data representing the input signal 12 and equalized output signal 192, respectively, of a closed-loop DGEF system 90 (similar to that in FIG. 13), which includes a DGEF similar to that shown in FIG. 1 having a micro-mirror device 100, as described hereinbefore, whereby the flipping of the micro-mirrors is controlled by the above described gain equalizing algorithm. FIG. 26 shows a 50 GHz WDM signal 12 having unequalized optical channels. FIG. 27 shows the resulting equalized output signal 192 of the DGEF system 90, whereby the error between each of the gain of each of the optical signals 14 is between +/−0.2 dB.
[0158]FIG. 30 illustrates another embodiment of DGEF 230 in accordance with the present invention, which is similar to the DGEF of FIG. 1, and therefore like components have the same reference numerals. Unlike the DGEF of FIG. 1, the DGEF 230 flip the micro-mirrors 52 of the spatial light modulator 36 to direct the equalized output signal 38 away from the return path 53 to thereby direct the output signal along optical path 56. The output signal 38 passes through a complimentary set of optics, such as a second bulk lens 234, a second λ/4 wave plate 235, a second diffraction grating 236, and a second collimating lens 238 to a second pigtail 240. Conversely, the attenuated portion of the light is reflected back through return path 53 to pigtail 22. An optical isolator 242 is provided at the input of the DGEF 230 to prevent this light from returning to the optical network.
[0167]FIG. 42 illustrates a schematic diagram of another embodiment of a dynamic optical filter 600 that provides improved sensitivity to tilt, alignment, shock, temperature variations and packaging profile. Similar to the filters described hereinbefore, the filter 600 includes a dual fiber pigtail 601 (circulator free operation), a collimating lens 26, a bulk diffraction grating 30, a Fourier lens 34, a λ/4 wave plate 35 and a spatial light modulator 100 (similar to that shown in FIG. 14). The dual fiber pigtail includes a transmit fiber 603 and a receive fiber 605.
A “well engineered” design must trade off the far-field beam size (large beam sizes allow for large physical δd but put high tolerances on the stability of the reflective assembly 618) and focal length and focal distance of the collimating lens 26. Conversely, small collimated beam sizes reduce the tolerances on the lens focal distance and relative stability of the retro-reflective object surfaces 618, but lead to larger angular errors δR (and hence larger power losses) as a function of assembly tilt θT.
[0180]FIG. 45 shows a perspective view of an embodiment of the chisel-shaped prism 604 that is use in combination with a spatial light modulator 100, such as a spatial light modulator manufactured by Texas Instruments (referenced hereinbefore and similar to that in FIG. 14) to provide the retro-reflection assembly. The prism 604 has two total internally reflecting (TIR) surfaces (the top surface 620 and back surface 622), and two transmissive surfaces (the front surface 624 and the bottom surface 626). The micro-mirror device 100 is placed normal to the bottom surface 626, as best shown in FIGS. 45 and 47.
[0181]FIG. 47 shows a practical embodiment of a tilt-insensitive reflective assembly 616 comprising the specially shaped prism 604 (referred as a “chisel prism”) and a micro-mirror device 100. Unlike an ordinary 45 degree total internal reflection (TIR) prism, in one embodiment the back surface of the prism is cut at approximately a 48 degree angle 621 relative to the bottom surface 626. The top surface is cut at a 4 degree angle 623 relative to the bottom surface to cause the light to reflect off the top surface via total internal reflection. The front surface 620 is cut at a 90 degree angle relative to the bottom surface. The retro-reflection assembly therefore provides a total of 4 surface reflections in the optical assembly (two TIRs off the back surface 622, one TIR off the micromirror device 100, and one TIR off the top surface 620.)
[0186]FIG. 48 illustrates to scale the channel layout and spacing of four optical channels of a WDM input signal onto the array of micromirrors of a micromirror device 100, similar to that described in FIGS. 14 and 21. The channels are substantially elliptical in shape and are disposed diagonally over the array of micromirrors. Note that only a intermediate portion of each of the optical channels is shown. The center of each channel is indicated by the axes c1-c4. In the example shown, the width of each channel W1-W4 is approximately equal and is approximately twice the spacing of the peaks of each of the optical channels. Consequently, the channels overlap spectrally. The left and right neighboring channels of any given channel have their 1/e2 intensity point at the center of the given channel, as best shown in FIG. 49.
[0188]FIG. 49 is a plot of the intensity of the optical channels of spectral channel layout of FIG. 48 taken along line 49-49 that illustrates four adjacent unmodulated channels on a 50 GHz (0.4 nm) spacing.
[0190]FIG. 50 illustrates the cause of the substantial loss resulting from pivoting the micromirrors 52 parallel to the spectral direction 55. Consequently, the micromirror device 100 is tilted at a predetermined angle α(e.g. 10 degrees) in the spatial plane 53. As a result, a deviation angle αd of the reflected light (i.e., shorter and longer wavelengths) is introduced that causes a wavelength dependant loss.
In contrast as shown in FIG. 50, the micromirrors 52 of the micromirror device 100 pivot perpendicular to the spectral direction 55. Consequently, the micromirror device 100 is tilted at a predetermined angle α(e.g., 10 degrees) in the spectral plane as best shown in FIGS. 1 and 50. As a result, as shown in FIG. 50, the deviation angle αd of the reflected light (i.e., shorter and longer wavelengths) is substantially zero such that a simple focal length shift (as shown in FIGS. 19a, 19 b) may be performed to compensate for the grating characteristics of the micromirror device.
[0192]FIG. 52 illustrates power loss versus wavelength of the embodiments described in FIGS. 50 and 51 across the “C” band and “L” band. The embodiment, wherein the micromirrors 52 have a pivot axis 52 perpendicular to the spectral direction 55, has minimal wavelength dependant loss, while the other embodiment, wherein the micromirrors have a pivot axis parallel to the spectral direction, has excessive wavelength dependant loss. Without some mitigation, the embodiment of FIG. 50 may preclude “C” band and “L” band operation.
[0193]FIG. 53 illustrates power loss versus wavelength of the embodiments described in FIGS. 50 and 51 across only the “C” band. Similar to that shown in FIG. 52, the parallel orientation of the pivot axis 52 shows significant wavelength dependant loss, while the perpendicular orientation shows minimal loss.
FIGS. 54-63 illustrate the mechanical design of an optical filter 640, similar to the optical filter 600 described in FIGS. 42-49. FIG. 54 is a perspective view of the optical filter 640 that includes a DSE controller 641, a controller 58, a programmable gate array 642, a pair of optical couplers 644, an optical assembly 646, which includes the optics shown in FIG. 42. The processor communicates with the controller through an electrical connector 648. Referring to FIG. 90, the DSE controller 641 includes a data acquisition and control device for processing input from chassis temperature sensors and micromirror device (DMD) 50 temperature sensor. The data acquisition and control device further controls a thermoelectric device (TEC) to cool the micromirror device. The DSE controller further includes a laser for imaging a reference signal on the micromirror device and a photodiode for sensing the light reflecting back from the micromirror device, which provides and indication of movement of failure of the micromirror device. As shown, a programmable gate array (FPGA) controls the flipping of the micromirrors in response to an algorithm and input signal. ;
[0195]FIG. 55 illustrates the optical assembly 640 includes the optics mounted to an optical chassis 650. The chassis includes a plurality of isolators to provide shock absorbers. The optics include a dual pigtail assembly 601, a collimating lens 26, a telescope 602 (e.g., cylindrical lens), a diffraction grating 30, a Fourier lens 34, a fold mirror 611, a wedge 608, a zero order wave plate 35,606, a chisel prism 604 and micromirror device 100 (not shown).
[0196]FIGS. 56 and 57 show the Fourier lens 34 and lens mount or retaining clip 652 that provides kinematic mounting of the Fourier lens. The mount includes a pair of finger stock springs 654 that urge the lens 34 upward against three posts disposed in the upper wall of the retaining spring 652. The mount further includes a pair of leaf springs 656 that urge the lens rearward against 3 posts or protrusions disposed in the rear wall of the clip. The mount is adjustable to the chassis to permit adjustment of the focal length before being welded thereto.
[0197]FIG. 58 shows the mounting mechanism for mounting the chisel prism 604 and the wedge 608 to the optical chassis 605. The wedge is mounted to a rod the passes through a bore in the chassis. The rod permits the wedge to be rotated about its longitudinal axis during assembly to align the retro-reflected light to the receive pigtail 605 (not shown), whereinafter the rod is secured to the chassis, such as by welding. The prism is secured to the chassis by a 6 point mount that include a retaining clip 660 and a pair of plungers 662.
[0198]FIGS. 59 and 60 show the diffraction grating 30 and grating mount 664 that provides kinematic mounting of the grating. The grating is disposed in the grating mount that includes two sets of finger stock springs 668,669 that urge grating against three tabs 670 disposed in the chassis and the protrusions 671 disposed in the upper wall of the mount 664. Further, a finger stock 672 is dispose in one side of the mount for urging the grating against the opposing side wall of the mount. The front surface 673 of the grating is ablated to remove the epoxy at 674 to provide a hard surface to engage the tabs 670 disposed in the chassis 605.
[0199]FIGS. 61 and 62 illustrate the telescope 602 that includes a pair of lens 676,677 mounted to a pair of submounts 678,679. An intermediate component permits the focal length of the pair of lens 676,677 and the rotational orientation therebetween to be adjusted off chassis. After being adjusted, the telescope can then be welded or otherwise secured to the chassis.
[0200]FIG. 63 shows a cross-section view of the collimating lens 26 that includes the dual fiber pigtail assembly 601 disposed therein. Similar to the telescope 602, the lens portion 680 may be rotated relative to the pigtail assembly 601 and the focal length therebetween adjusted.
As shown in FIGS. 65-67, an optical filter, generally shown as 700, is programmable to selectively provide a desired filter function for filtering an optical WDM input signal 12 in network applications, for example. The flexible optical filter includes a micromirror device similar to the DGEF shown in FIGS. 1-64, which is described in great detail hereinafter. In fact the configuration of the flexible optical filter 700 is substantially the same as the DGEF described hereinafter. The digital signal processor (DSP) (see FIG. 77) of the controller 58 or DSE controller of optical filter 700 is programmable to provide any desirable filter function in response to control signal 702 at input 704. Alternatively, the DSP may be programmed to provide the desired filter function. The control signal is provided to the controller 58 (see FIG. 2) of the micromirror device 36. In response to the control signal 702, the controller 58 flips the appropriate mirror or mirrors 52 to provide the desired filter function.
For example as shown in FIG. 65, the optical filter 702 may selectively attenuate selected optical channel(s) of an input signal 706 to flatten or equalize each of the input channels to provide an equalized output signal 708, as described hereinafter in FIGS. 1-64.
As shown in FIG. 67, the optical filter 700 may be reconfigured to function as an optical spectral analyzer (OSA) functioning in the scan mode. A WDM input signal 710 is provided at the input port 712. In response to the control signal 702, the micromirrors 52 are dynamically flipped to sequentially drop each of the input optical channels at the output port 720. The output may then be provided to an optical detector (not shown) to measure and determine various optical characteristics of the input signal. This configuration is also similar to the optical channel monitor (OCM) of copending U.S. Provisional Patent Application Serial No. (Cidra Docket No. CC-0396), which is incorporated herein by reference.
In this scanning mode one will also appreciate that as the filter function scans the spectrum of the input signal, the bandwidth may be varied to provide data to measure the optical signal-to-noise (OSNR) of the input signal or channels, as described in U.S. Provisional Patent Application Serial No. (CC-0369), which is incorporated herein by reference. For instance, a filter function having a wide bandwidth is used to measure the power of an optical channel, while a filter function having a narrow bandwidth is used to measure the noise level between the optical channels.
As shown in FIG. 68, the optical filter 730 provides a pair of output ports 732,733, which is similar to the reconfigurable optical add/drop multiplexer (ROADM) described in U.S. Provisional Patent Application No. (CC-0381), which is incorporated herein by reference. In response to the control signal 702, the optical filter 730 drops a channel or group of channels to one output port 732, and redirects the other output signals to the second port 734. One will appreciate that the two-port optical filter 730 may be configured to function as the optical filters in FIGS. 65-67.
As shown in FIG. 69, the optical filter 730 provides a pair of output ports 732, 733, which is similar to the optical interleaver/deinterleaver (ROADM) described in U.S. Provisional Patent Application Serial No. (CC-0397), which is incorporated herein by reference. In response to the control signal 702, the optical filter 730 drops all the odd channels one output port 732, and redirects all the even output signals to the second port 734. One will appreciate that the two-port optical filter 740 may be configured to function as the optical filters in FIGS. 65-67.
In FIG. 72, the optical filter 720, 730, having a pair of output ports 732, 734, may function as a programmable edge filter.
The optical filters 700, 720, 730 may also be configured to provide a variable or selectable filter shape, such as sawtooth, ramp and square. The optical filters 720, 730 may also be configured to tap off selected portions of the input signals at one output port and pass the remaining portions of the input signal through the second output port.
One example of having a transmissive state and an absorptive state is Heterojunction Acoustic Charge Transport (HACT) Spatial Light Modulator (SLM) technology, such as that described in U.S. Pat. No. 5,166,766, entitled “Thick Transparent Semiconductor Substrate, Heterojunction Acoustic Charge Transport Multiple Quantum Well Spatial Light Modulator”, Grudkowski et al and 5,158,420, entitled “Dual Medium Heterojunction Acoustic Charge Transport Multiple Quantum Well Spatial Light Modulator” to Grudkowski et al, provided the material used for the HACT SLM will operate at the desired operational wavelength. In that case, the pixels may be controlled by charge packets that travel along a surface acoustic wave that propagates along the device, where the size of the charge controls the optical absorption.
US6671295 * Aug 27, 2001 Dec 30, 2003 Interscience, Inc. Tunable diode laser system, apparatus and method
US6983090 * Mar 11, 2003 Jan 3, 2006 Jds Uniphase Inc. High resolution tunable optical filter
US7043110 * Dec 10, 2002 May 9, 2006 Silicon Light Machines Corporation Wavelength-selective switch and equalizer
US7103258 Oct 24, 2005 Sep 5, 2006 Nikon Corporation Attenuator device, and optical switching device
US7292749 * Oct 15, 2002 Nov 6, 2007 Danmarks Tekniske Universitet System for electromagnetic field conversion
US8094982 * Jan 15, 2008 Jan 10, 2012 Oclaro (North America), Inc. Fiber lens assembly for optical device
US8463125 * Sep 9, 2010 Jun 11, 2013 Santec Corporation Optically variable filter array apparatus
US8463126 * Sep 9, 2010 Jun 11, 2013 Santec Corporation Optically variable filter array apparatus
US8488229 * Feb 2, 2011 Jul 16, 2013 Santec Corporation Method for calibration of optically variable filter array apparatus
US9372311 Sep 17, 2014 Jun 21, 2016 Sumitomo Electric Industries, Ltd. Wavelength selective switch
US9374563 * Nov 1, 2012 Jun 21, 2016 Raytheon Company Multispectral imaging camera
US20060039669 * Oct 24, 2005 Feb 23, 2006 Nikon Corporation Attenuator device, and optical switching device
US20060159395 * Dec 15, 2005 Jul 20, 2006 Alan Hnatiw Optical compensator array for dispersive element arrays
US20080018983 * Jul 11, 2007 Jan 24, 2008 Fusao Ishii Color display system for reducing a false color between each color pixel
US20080219619 * Jan 15, 2008 Sep 11, 2008 Xuehua Wu Fiber lens assembly for optical device
US20110268445 * Sep 9, 2010 Nov 3, 2011 Yasuki Sakurai Optically variable filter array apparatus
US20110293281 * Sep 9, 2010 Dec 1, 2011 Yasuki Sakurai Optically variable filter array apparatus
US20120154893 * Feb 2, 2011 Jun 21, 2012 Yuji Hotta Method for calibration of optically variable filter array apparatus
US20140118604 * Nov 1, 2012 May 1, 2014 Raytheon Company Multispectral imaging camera
US20150311996 * May 19, 2014 Oct 29, 2015 Fundacao Cpqd - Centro De Pesquisa E Desenvolvimento Em Telecomunicacoes Systems and methods for global spectral equalization
WO2004097496A1 * Apr 23, 2004 Nov 11, 2004 Nikon Corporation Attenuator device and optical switching device
International Classification G02B27/10, H04Q11/00, G02B6/34, G02B26/08, H04J14/02, G02B6/35
Cooperative Classification H04J14/0221, H04J14/021, G02B6/29311, H04Q2011/0018, G02B6/29398, H04Q2011/0009, G02B6/359, G02B6/3516, G02B27/1006, G02B6/29395, G02B6/29394, G02B6/2931, G02B6/29313, G02B27/1086, G02B27/1073, G02B6/278, G02B26/0841, H04Q2011/0026, G02B6/3588, H04J14/0213, G02B6/29314, G02B6/356
European Classification G02B6/293D2V, G02B6/293D2V2, G02B6/27W8, G02B27/10M, G02B6/293W10, G02B27/10Z, G02B27/10A, H04J14/02B, G02B26/08M4E, G02B6/35N8, G02B6/293W8C, G02B6/293D2T, G02B6/293D2R, G02B6/293W14
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:DAVIS, M.;KERSEY, A.;MOON, J.;AND OTHERS;REEL/FRAME:013137/0180