(19) United States
`(12) Patent Application Publication (10) Pub. No.: US 2002/0097956 A1
`Kikuchi et al.
`(43) Pub. Date:
`Jul. 25, 2002
`
`US 20020097956A1
`
`(54) FIBER COLLIMATOR ARRAY
`
`Publication Classification
`
`(76)
`
`Inventors: Juro Kikuchi, Kakegawa-City (JP);
`Yasuyuki Mizushima, Kakegawa-City
`(JP); Hiroki Takahashi, Fukuroi City
`(JP); Yoshiaki Takeuchi, Shizuoka-shi
`(JP)
`
`Correspondence Address:
`CORNING INCORPORATED
`SP-TI-3-1
`
`CORNING, NY 14831
`
`(21) Appl. No.:
`
`09/767,255
`
`(22)
`
`Filed:
`
`Jan. 22, 2001
`
`Int. Cl.7 ..................................................... .. G02B 6/32
`(51)
`(52) U.S.Cl.
`............................................... -335/33; 385/34
`
`(57)
`
`ABSTRACT
`
`An optical fiber collimator array includes an optical fiber
`array block and a microlens array substrate. The optical fiber
`array block includes an angled surface and is configured to
`receive and retain a plurality of individual optical fibers,
`which carry optical signals. The microlens array substrate
`includes a plurality of microlenses integrated along a micro-
`lens surface and a sloped surface opposite the microlens
`surface. The microlens surface is coupled to the angled
`surface such that the optical signals from the individual
`optical fibers are each collirnated by a different one of the
`integrated microlenses.
`
`116
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`
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`FNC 1023
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`Patent Application Publication
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`Jul. 25, 2002 Sheet 1 of 5
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`FIG. 1B
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`Patent Application Publication
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`Patent Application Publication
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`Jul. 25, 2002 Sheet 5 of 5
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`832
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`834
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`FIG. 9B
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`US 2002/0097956 A1
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`Jul. 25, 2002
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`FIBER COLLIMATOR ARRAY
`
`BACKGROUND OF THE INVENTION
`
`[0001]
`
`1. Field of the Invention
`
`[0002] The present invention is directed to a fiber colli-
`mator array and more specifically to a fiber collimator array
`for use in an optical transmission system and/or an optical
`sensor system.
`
`[0003]
`
`2. Technical Background
`
`[0004] Collimation is a process by which divergent beams
`of radiation or particles (e.g., light rays) are converted into
`parallel beams. Laser diode (LD) collimating lenses are
`commonly used in laser beam printers, bar code scanners
`and sensors. In addition, fiber collimators are widely used in
`a variety of optical applications (e.g., optical filters). Due to
`the recent increase in demand for fiber collimators, to be
`used with wave division multiplexed (WDM) systems,
`reducing the fiber collimator cost has become increasingly
`important.
`
`[0005] However, commercially available fiber collimator
`arrays have typically implemented separate lenses, which
`has increased the cost of the array. For example, one
`commercially available collimator array has utilized a
`V-groove array substrate with individually aligned gradient-
`index (GRIN) microlenses and fibers in each V-groove.
`These GRIN microlenses have generally been produced by
`an ion-exchange process and normally provide high cou-
`pling efficiency and have been utilized as collimators for
`laser beam printers, bar code scanners, optical isolators,
`circulators and digital versatile disc (DVD) players, as well
`as miniature objective lenses for medical/industrial endo-
`scopes.
`
`[0006] Planar microlens arrays (PMLAs) are two-dimen-
`sional GRIN-type lens arrays that integrate ion-exchange
`technology and photolithography. By diffusing ions through
`a photolithographic mask into a glass substrate, numerous
`microscopic lenses can be formed in various sizes and
`patterns. Commercially available PMLAs are available with
`swelled lens surfaces, which tend to increase coupling
`efficiencies in transceiver applications, or with fiat surfaces,
`which typically simplify collimation with fiber arrays.
`PMLAs have been used in liquid crystal projectors, three
`dimensional data processing and two dimensional
`laser
`diode (LD) coupling to fibers. Other manufactures, such as
`Rochester Photonics Corp., have produced aspheric colli-
`mating microlenses that are intended to replace GRIN-type
`microlenses in collimating applications.
`
`[0007] However, the effectiveness of GRIN-type PMLAs
`and collimating arrays incorporating aspheric collimating
`microlenses are highly dependent on the configuration of the
`fiber collimator array. As such, it is important to configure
`the fiber collimator array to reduce insertion loss and inter-
`nal reflections.
`
`SUMMARY OF THE INVENTION
`
`[0008] An embodiment of the present invention is directed
`to an optical fiber collimator array that includes an optical
`fiber array block and a microlens array substrate. The optical
`fiber array block includes an angled surface and is config-
`ured to receive and retain a plurality of individual optical
`
`fibers, which carry optical signals. The microlens array
`substrate includes a plurality of microlenses integrated along
`a microlens surface and a sloped surface opposite the
`microlens surface. The microlens surface is coupled to the
`angled surface such that the optical signals from the indi-
`vidual optical fibers are each collimated by a different one of
`the integrated microlenses.
`
`[0009] According to another embodiment of the present
`invention, an optical fiber collimator array includes an
`optical fiber array block, a microlens array substrate and an
`index-matched spacer. The optical fiber array block is con-
`figured to receive and retain a plurality of individual optical
`fibers, which carry optical signals. The microlens array
`substrate includes a plurality of microlenses integrated along
`a microlens surface and the index-matched spacer couples
`the optical fiber array block to the microlens array substrate.
`
`[0010] Additional features and advantages of the inven-
`tion will be set forth in the detailed description which
`follows and will be apparent to those skilled in the art from
`the description or recognized by practicing the invention as
`described in the description which follows together with the
`claims and appended drawings.
`
`It is to be understood that the foregoing description
`[0011]
`is exemplary of the invention only and is intended to provide
`an overview for the understanding of the nature and char-
`acter of the invention as it is defined by the claims. The
`accompanying drawings are included to provide a further
`understanding of the invention and are incorporated and
`constitute part of this specification. The drawings illustrate
`various features and embodiments of the invention which,
`together with their description, serve to explain the princi-
`pals and operation of the invention.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`[0012] FIG. 1A is a cross-sectional view of an optical
`fiber collimator array, according to an embodiment of the
`present invention;
`
`[0013] FIG. 1B is a top plan view of the array of FIG. 1A;
`
`[0014] FIG. 1C is a cross-sectional view of an optical
`fiber collimator array, according to another embodiment of
`the present invention;
`
`[0015] FIG. 2 is a cross-sectional view of the collimator
`array of FIG. 1A that additionally includes an index-
`matched angled spacer;
`
`[0016] FIG. 3 is a cross-sectional view of another embodi-
`ment of an optical fiber collimator array of the present
`invention;
`
`[0017] FIG. 4 is a cross-sectional view of yet another
`embodiment of an optical fiber collimator array of the
`present invention;
`
`[0018] FIG. 5 is a cross-sectional view of still another
`embodiment of an optical fiber collimator array of the
`present invention;
`
`[0019] FIG. 6 is a cross-sectional view of a different
`embodiment of an optical fiber collimator array of the
`present invention;
`
`[0020] FIGS. 7A-7C are cross-sectional views of the opti-
`cal fiber collimator array of FIG. 6 during assembly;
`
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`[0021] FIG. 8 is a cross-sectional view of an optical fiber
`collimator array that utilizes a spacer with a hole;
`
`taken through
`[0022] FIGS. 9A-9B are cross-sectional,
`sectional line IXA, and end elevational views, respectively,
`of the spacer of FIG. 8; and
`
`[0023] FIG. 10 is a cross-sectional view of a microlens
`array substrate with a non-fiat lens surface.
`
`DETAILED DESCRIPTION OF THE
`
`PREFERRED EMBODIMENT(S)
`
`[0024] The present invention is directed to an optical fiber
`collimator array that includes a microlens array substrate
`and an optical fiber array block that are configured to reduce
`insertion loss and to reduce internal reflections. Each micro-
`
`lens is preferably a graded-index (GRIN) lens, an aspheric
`lens or a Fresnel lens. A GRIN lens has a refractive index
`
`that decreases with distance from its optical axis (i.e.,
`center). This causes light rays to travel in sinusoidal paths,
`with the length of one complete cycle being known as the
`pitch of the lens. Commercially available fiber array blocks
`typically have a pitch of either two-hundred fifty microns or
`one-hundred twenty-seven microns. The pitch of the fiber
`block limits the microlens diameter, which may limit the
`coupling efficiency of the lens since the modefield diameter
`of the optical power (of the optical signal) in the microlens
`plane is limited by the microlens diameter.
`
`[0025] To reduce coupling loss to less than 0.01 dB, the
`modefield diameter should typically be less than half the
`effective microlens diameter. As such, when a GRIN lens
`with a pitch of two-hundred fifty microns is used,
`the
`modefield diameter should be less than one-hundred ten
`
`microns since the effective lens diameter is typically less
`than ninety percent of the physical lens diameter. While a
`larger collimated beam diameter is preferable in order to get
`higher coupling efficiency, at typical working distances over
`a few millimeters, in practical use, the modefield diameter
`limits the diameter of the collimated optical beam. As such,
`the dimensions of the fiber collimator array, including the
`optical fiber array block and the microlens array substrate,
`are limited. Preferably, the modefield diameter of an optical
`signal on a microlens plane should be set close to one-
`hundred ten microns.
`
`[0026] Turning to FIGS. 1A-1B, a cross-sectional and top
`plan view, respectively, of an optical fiber collimator array
`100, according to an embodiment of the present invention,
`are depicted. The array 100 retains a plurality of optical
`fibers 108 within an optical fiber array block 102, which
`includes a plurality of channels for receiving the fibers 108,
`which are preferably retained within the block 102 with an
`adhesive. A planar graded-index (GRIN) microlens array
`substrate 104 includes a plurality of GRIN microlenses 106,
`which are spaced such that each microlens 106 receives an
`optical signal from one of the optical fibers 108. The fiber
`array block 102 includes an angled surface 112, opposite the
`end of the fiber block 102 in which the fibers 108 enter the
`
`fiber block 102. The microlens array substrate 104 includes
`a sloped surface 114 opposite the microlenses 106 (i.e., a
`microlens surface 116). The angled surface 112, of the fiber
`array block 102, and the sloped surface 114, of the microlens
`array substrate 104, are designed to reduce reflection at the
`boundary between the block 102 and the substrate 104.
`Preferably, the microlens array substrate 104 is made of a
`
`glass (e.g., PYREX®) and one end of the fibers 108 are fixed
`flush with and have substantially the same angle as the
`angled surface 112.
`
`[0027] The block 102 and the substrate 104 are preferably
`joined to each other through the use of a commercially
`available index-matched optical adhesive 110A, preferably
`using an active alignment tool. Suitable UV-cured index-
`matched optical adhesives are commercially available from
`NTT Advanced Technology Corporation (e.g., product num-
`ber 9389 is suitable for a refractive index of 1.448). If
`desired, a conventional anti-reflection
`coating or coat-
`ings 110B may also be added to the interface between the
`block 102 and the substrate 104. The angles (i.e., the angled
`surface 112 and the sloped surface 114) are preferably eight
`degrees from perpendicular to the optical axes of the fibers
`108, which,
`in theory, should provide at
`least a 60 dB
`attenuation of any reflected signal. Refiections can also be
`further reduced at the microlens surface 116 by applying an
`AR coating (or a multi-layer AR coating) 117 to the surface
`116. However, utilizing an AR coating 117 with the micro-
`lens array substrate 104, of FIG. 1A, has been shown to only
`reduce reflections to about one-tenth of one percent of the
`transmitted signal (i.e., about 30 dB). While a return loss of
`30 dB is acceptable in many applications, such a return loss
`is generally not acceptable in some practical applications,
`such as fiber amplifier modules.
`
`[0028] FIG. 1C illustrates a cross-sectional view of an
`optical fiber collimator array 120, according to another
`embodiment of the present invention, that retains a plurality
`of optical fibers 128 within an optical fiber array block 122.
`The fiber collimator array 120 can typically achieve a return
`loss greater than 60 dB when AR coatings are utilized. An
`aspheric microlens array substrate 124 includes a plurality of
`aspheric microlenses 126, which are spaced such that each
`microlens 126 receives an optical signal from one of the
`optical fibers 128. The fiber array block 122 includes an
`angled surface 132, opposite the end of the fiber block 122
`in which the fibers 128 enter the block 122. The microlens
`
`array substrate 124 includes a sloped surface 134 opposite
`the microlenses 126 (i.e., a microlens surface 136). The
`angled surface 132 of the fiber array block 122 and the
`sloped surface 134 of the microlens array substrate 124 are
`designed to reduce reflection at the boundary between the
`block 122 and the substrate 124. Preferably, the microlens
`array substrate 124 is also made of a glass (e.g., PYREX®).
`
`[0029] The block 122 and the substrate 124 are preferably
`attached to each other through the use of an index-matched
`optical adhesive 130A, preferably using an active alignment
`tool, and may included an AR coating (or coatings) 130B at
`the interface. Similar to the collimator array 100 of FIG. 1A,
`the angles of the block 122 and substrate 124 are preferably
`eight degrees from perpendicular to the optical axes of the
`fibers 128. Refiections can also be further reduced by
`applying an anti-reflection
`coating 127 to the micro-
`lens surface 136.
`
`[0030] The reflections of the array 100 can be further
`reduced through the implementation of an index-matched
`angled spacer. As shown in FIG. 2, an optical fiber colli-
`mator array 200 includes an index-matched angled spacer
`202, which reduces reflections at the microlens surface 116
`of the GRIN microlens array substrate 104. Preferably, the
`angled spacer 202 is attached to the microlens surface 116,
`
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`of the array substrate 104, with an index-matched optical
`adhesive 204, after active alignment of the microlens array
`104 with the fiber array block 102. The refractive index of
`the spacer 202 is preferably selected to be substantially the
`same as that of the microlens 106. When another device,
`such as an optical filter, is not directly connected to the
`spacer 202, a slanted surface 206 of the spacer 202, opposite
`that attached to the microlens array substrate 104, is also
`preferably coated with an AR coating 205 to further reduce
`reflection. Typically, a slant of less than about one degree is
`enough for the spacer 202 to adequately attenuate any
`reflections (i.e., at least a 60 dB loss).
`
`In the fiber collimator arrays 100, 120 and 200 of
`[0031]
`FIGS. 1A-1C and 2, respectively,
`the optical beam axis
`generally slightly slants at the boundary of the fiber array
`block and the microlens array substrate when the refractive
`index of the materials (i.e., the fiber core and substrate) differ
`from each other. As such,
`the coupling efficiency of an
`optical system,
`that includes such a collimator array,
`is
`slightly degraded. This is because the modefield center of
`optical power in the microlens plane slightly shifts from the
`center of the microlens. This slight shift adversely affects the
`coupling efficiency, since the whole optical beam modefield
`is very close to the effective microlens area.
`
`[0032] Moving to FIG. 3, a cross-sectional view of an
`optical fiber collimator array 300, according to yet another
`embodiment of the present invention, is depicted. In general,
`the fiber collimator array 300 provides a higher coupling
`efficiency as compared to the fiber collimator arrays of
`FIGS. 1A-1C and 2. As shown in FIG. 3, an optical fiber
`array block 302 retains a plurality of optical fibers 308. An
`angled surface 312 of the fiber array block 302 is coupled
`(preferably, with an index-matched optical adhesive 310A)
`to a sloped surface 314 of a GRIN microlens array substrate
`304. If desired, an AR coating 310B may also be provided
`at the interface between the block 302 and the substrate 304.
`
`The sloped surface 314 of the microlens array substrate 304
`is preferably formed at an angle that is different from the
`angled surface 312 of the fiber array block 302.
`
`[0033] The center angle of the sloped surface 314 of the
`microlens array substrate 304 is, preferably, adjusted to be a
`somewhat different value from 8+/-0.5 degrees, depending
`on the difference of the refractive index of the core of fibers
`
`308 and the microlens array substrate 304. If the refractive
`index of the microlens array substrate 304 is 1.66, for
`example, an appropriate center angle is about 83 degrees.
`The microlens array substrate 304 is adjusted in relation to
`the block 302 such that the optical beam axis coincides with
`the optical axis (i.e., center) of each of the microlenses 306.
`In this configuration,
`the reflection from the microlens
`surface 316 can be reduced by using an index-matched
`optical adhesive 318 and by attaching an index-matched
`angled spacer 332 that includes an AR coating 336 on its
`slanted surface 334. A back surface 330 of the spacer 332
`does not require an AR coating, since the index of the spacer
`332 preferably matches that of the microlens 306. A similar
`configuration can also be utilized in conjunction with an
`aspheric microlens array substrate, such as that of FIG. IC.
`
`[0034] A preferred material for the optical fiber array
`blocks of FIGS. 1A-1C, 2 and 3 is PYREX® or silicon glass,
`which is selected to match the coefficient of thermal expan-
`sion (CTE) of the microlens array substrate material. That is,
`
`if the microlens array substrate is made of silica glass, the
`same material (silica glass) would be a preferred choice for
`the material of the fiber array block.
`
`[0035] FIG. 4 depicts a cross-sectional view of an optical
`fiber collimator array 400, according to still another embodi-
`ment of the present invention. In general, the fiber collimator
`array 400 provides an alternative to the fiber collimator array
`300 that is particularly useful when alignment of the block
`302 and substrate 304 is burdensome or when the thickness
`
`of the substrate 304 cannot be easily controlled to within
`about ten microns. As shown in FIG. 4, a fiber array block
`402 retains a plurality of optical fibers 408. An angled
`surface 412 of the fiber array block 402 is coupled (e.g., with
`an index-matched optical adhesive 410A) to a slanted sur-
`face 434 of an index-matched angled spacer 432. If desired,
`an AR coating 410B may also be provided at the interface
`between the block 402 and the spacer 432. The spacer 432
`includes a back surface 430 that is opposite the slanted
`surface 434. The slanted surface 434 of the spacer 432 is
`preferably formed at an angle that is different from the
`angled surface 412, of the fiber array block 402. A back
`surface 414 of the microlens array substrate 404 is then
`adjusted in relation to the back surface 430, of the spacer
`432, such that each optical beam axis coincides with an
`optical axis of one of the microlenses 406. When proper
`alignment is achieved between the substrate 404 and the
`spacer 432, the two are coupled together, preferably, with an
`index-matched optical adhesive 420. In this configuration,
`the reflection from the microlens surface 416, of the micro-
`lens array substrate 404, can be reduced by adding an AR
`coating 418 to the surface 416.
`
`[0036] FIG. 5 illustrates a cross-sectional view of an
`optical fiber collimator array 500, according to a different
`embodiment of the present invention. In the embodiment of
`FIG. 5, all surfaces of the array 500, that an optical beam
`crosses, are substantially perpendicular, at least initially, to
`the optical axis of each microlens 506. A fiber array block
`502 retains a plurality of optical fibers 508 and includes a
`first surface 512 that is coupled (e.g., with an index-matched
`optical adhesive 511) to a first surface 534 of an index-
`matched spacer 532. The spacer 532 includes a second
`surface 530 that is opposite the first surface 534. Amicrolens
`surface 516 of the microlens array substrate 504 is then
`adjusted in relation to the second surface 530 such that the
`optical beams coincide with the optical axis of each of the
`microlenses 506.
`
`[0037] When proper alignment is achieved between the
`substrate 504 and the spacer 532, they are coupled together,
`preferably, with an index-matched optical adhesive 513A. If
`desired, an AR coating 513B may also be provided at the
`interface between the spacer 532 and the substrate 504. The
`refractive index of the spacer 532 is preferably matched to
`the refractive index of the core of the optical fiber 508. A
`reflection reduction of approximately 20 dB is achievable
`due to the spacing, dictated by the width (dependent on the
`focal length of the microlenses 506) of the spacer 532,
`between the ends of the optical fibers 508 and the micro-
`lenses 506. This is because the modefield of an optical beam
`from each of the fibers 508 diverge until they reach one of
`the microlenses 506. In this configuration,
`the reflection
`from the microlens surface 516 of the microlens array
`substrate 504 can be reduced by adding anAR coating 513B
`to the interface between the spacer 532 and the substrate
`
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`504. Further, the reflection from a back surface 514 of the
`array 504, opposite the microlens surface 516, can be
`reduced by adding anAR coating 515 to the surface 514 and
`further reduced by angle polishing the surface 514.
`
`[0038] FIG. 6 illustrates a cross-sectional view of an
`optical fiber collimator array 600, according to another
`embodiment of the present invention. An optical fiber array
`block 602 retains a plurality of optical fibers 608 and
`includes an angled surface 612 that is coupled (e.g., with an
`index-matched optical adhesive 611A) to a slanted surface
`634 of an index-matched spacer 632. If desired, an AR
`coating 611B may also be provided at the interface between
`the spacer 632 and the block 602. The spacer 632 includes
`a back surface 630, opposite the angled surface 634, that is
`generally perpendicular to the optical axes of microlens 606.
`A microlens surface 616, of the microlens array substrate
`604, is then adjusted in relation to the surface 630, of the
`spacer 632, such that the optical beams coincide with the
`optical beam axis of each of the microlenses 606.
`
`[0039] When proper alignment is achieved between the
`substrate 604 and the spacer 632, they are coupled together,
`preferably, with an index-matched optical adhesive 613. The
`refractive index of the spacer 632 is, preferably, matched to
`the refractive index of the microlens 606. Further, any
`reflection from the surface 614 of the array 604, opposite the
`microlens surface 616, can generally be reduced by angle
`polishing the surface 614 and normally further reduced by
`adding an AR coating 615 to the surface 614.
`[0040] FIGS. 7A-7C illustrate a simplified procedure for
`fabricating the fiber collimator array 600 of FIG. 6. As
`shown in FIG. 7A, initially, the slanted surface 634 of the
`index-matched spacer 632 is attached to the angled surface
`612 of the optical fiber array block 602. The effective
`thickness (i.e., the length of the optical path in the spacer
`632) is passively adjusted using an alignment tool. Next, as
`is shown in FIG. 7B,
`the microlens surface 616 of the
`microlens array substrate 604 is actively aligned, preferably
`by using a mirror, with the back surface 630 of the spacer
`632. When proper alignment is achieved, the spacer 632 and
`microlens array substrate 604 are fixed in relation to one
`another with an index-matched optical adhesive 613.
`Finally, as shown in FIG. 7C, the back surface 614 of the
`substrate 604 is angle polished and AR coated 615,
`if
`required for the application.
`[0041] FIG. 8 depicts a cross-sectional view of a fiber
`collimator array 800, according to yet another embodiment
`of the present invention. A fiber array block 802 retains a
`plurality of optical fibers 808 and includes an angled surface
`812. A slanted surface 834 of a spacer 832 is adjusted with
`respect to the angled surface 812 until the optical beams
`provided through the optical fibers 808 are perpendicular to
`a back surface 830 of the spacer 832. The block 802 and the
`spacer 832 are then fixed with an adhesive 811B. If desired,
`an AR coating 811A may also be utilized on the surface 812
`of the block 802 to reduce reflections. A microlens surface
`
`816 of the microlens array substrate 804 is then adjusted in
`relation to the surface 830 of the spacer 832 such that the
`optical beams coincide with the optical beam axis of each of
`the microlenses 806. Preferably, the spacer 832 has a hole
`809, which allows the optical beams to pass from the ends
`of the optical fibers 808, through air, to the microlens 806.
`[0042] When proper alignment is achieved between the
`substrate 804 and the spacer 832, they are coupled together,
`
`with an adhesive 813A. However, in this embodiment an
`index-matched optical adhesive is not required since the
`optical beams travel through air. In this configuration, any
`reflection from the microlens surface 816, of the microlens
`array 804, can also typically be reduced by adding an AR
`coating 813B to the surface 816. Reflections from the
`surface 814, opposite the microlens surface 816, can also
`typically be reduced by angle polishing the surface 814 and
`by adding an AR coating 815 to the surface 814, if required
`for the application.
`
`[0043] When a spacer is located between the fiber array
`block and the microlens array substrate, as shown in FIGS.
`4, 5, 6, 7A-7C and 8, it is desirable to CTE match the spacer
`with the fiber array block and the microlens array substrate
`for high property stability over a wide temperature range.
`Preferably,
`the spacer material is a glass material that is
`transparent in the applied wavelength range, except in the
`case of FIG. 8, the spacer material does not have to be
`transparent
`in the applied wavelength range. The glass
`material of the angled spacer of FIG. 4 is, preferably,
`selected to match the refractive index of the microlens array
`substrate. The glass material of the angled spacer of FIGS.
`2, 3, 6 and 7A-7C is, preferably, selected to match the
`refractive index of the microlens.
`
`[0044] A suitable angle for the angled surface of the fiber
`array blocks of FIGS. 1A-1C, 2, 3, 4, 6, 7A-7C and 8 is
`about 8+/-0.1 degrees. It should be appreciated that the
`angle range is a function of the desired minimum reflection.
`For example, if a center angle of 8.5 degrees is utilized, a
`wider angular range of about +/-0.6 degrees provides an
`acceptable reflection reduction. An acceptable angle for the
`sloped surface of the microlens array substrate is about
`8+/-0.5 degrees. However, the angle of the sloped surface
`can typically vary somewhat as the position of the microlens
`array substrate to the fiber array block is adjusted actively in
`the fiber collimator array fabrication process. In the case of
`the array of FIG. 3, the center angle of the sloped surface is
`preferably adjusted to be a slightly different value from
`8+/-0.5 degrees, depending on the refractive index differ-
`ence between the core of the fiber and the microlens array
`substrate. Asimilar angular range of +/-0.5 degrees from the
`center angle is also usually acceptable for the slanted surface
`of the angled spacers of FIGS. 4, 6, 7A-7C and 8. In the case
`of FIGS. 6, 7A-C and 8, the back surface of the microlens
`array substrate is, preferably, angle polished to an angle of
`1+/-0.5 degrees, since a minimum angle of 0.4 degrees
`reduces the reflectivity such that the collimator array attenu-
`ates reflections by at least about 60 dB. The back surface of
`the index-matched angled spacers of FIGS. 2 and 3 are also
`preferably angle polished to an angle of about 1+/-0.5
`degrees for similar reasons.
`
`[0045] FIGS. 9A-9B show a cross-sectional view and a
`side view, respectively, of an exemplary spacer 832 that can
`be utilized in the array of FIG. 8. As previously discussed,
`with respect to FIG. 8, the slanted surface 834 is adjusted
`such that the back surface 830, which faces the substrate, is
`perpendicular to the optical beams provided by the optical
`fibers 808. FIG. 10 depicts a microlens array 900 with a
`non-flat lens surface 902 that can be utilized with many of
`the embodiments, disclosed herein. Further, while only
`linear arrays have been depicted, one of ordinary skill in the
`art will appreciate that
`the arrays, disclosed herein, can
`readily be expanded to two-dimensional arrays.
`
`

`
`US 2002/0097956 A1
`
`Jul. 25, 2002
`
`In summary, an optical fiber collimator array has
`[0046]
`been described that includes an optical fiber array block and
`a microlens array substrate. The optical fiber array block
`includes an angled surface and is configured to receive and
`retain a plurality of individual optical fibers, which carry
`optical signals. The microlens array substrate includes a
`plurality of microlenses integrated along a microlens surface
`and a sloped surface opposite the microlens surface. The
`microlens surface is coupled to the angled surface such that
`the optical signals from the individual optical fibers are each
`collimated by a different one of the integrated microlenses.
`According to another embodiment of the present invention,
`an optical fiber collimator array includes an optical fiber
`array block, a microlens array substrate and an index-
`matched spacer. The optical fiber array block is configured
`to receive and retain a plurality of individual optical fibers,
`which carry optical signals. The microlens array substrate
`includes a plurality of microlenses integrated along a micro-
`lens surface and the index-matched spacer couples the
`optical fiber array block to the microlens array substrate.
`
`It will become apparent to those skilled in the art
`[0047]
`that various modifications to the preferred embodiment of
`the invention as described herein can be made without
`
`departing from the spirit or scope of the invention as defined
`by the appended claims.
`The invention claimed is:
`
`1. An optical fiber collimator array, comprising:
`
`an optical fiber array block configured to receive and
`retain a plurality of individual optical fibers which
`carry optical signals,
`the optical fiber array block
`including an angled surface; and
`
`a microlens array substrate including a plurality of micro-
`lenses integrated along a microlens surface, the micro-
`lens array substrate including a sloped surface opposite
`the microlens surface that is coupled to the angled
`surface such that the optical signals from the individual
`optical fibers are each collimated by a different one of
`the integrated microlenses.
`2. The collimator array of claim 1, wherein the integrated
`microlenses are graded-index (GRIN) lenses.
`3. The collimator array of claim 1, wherein the integrated
`microlenses are aspheric lenses.
`4. The collimator array of claim 1, wherein the integrated
`microlenses are Fresnel lenses.
`
`5. The collimator array of claim 1, wherein the sloped
`surface of the microlens array substrate is coupled to the
`angled surface of the optical fiber array block by an index-
`matched optical adhesive.
`6. The collimator array of claim 1, wherein the microlens
`surface includes an anti-reflection
`coating.
`7. The collimator array of claim 1, wherein the pitch of the
`integrated microlenses is about 250 microns.
`8. The collimator array of claim 1, wherein the sloped
`surface of the microlens array substrate and the angled
`surface of the optical fiber array block are both at about eight
`degrees from perpendicular to the optical axes of the indi-
`vidual optical fibers.
`9. The collimator array of claim 1, further including:
`
`an index-matched angled spacer including a slanted sur-
`face and a perpendicular surface opposite the sla