WO2010118290A1

WO2010118290A1 - Stackable emitter prism assembly and method of use

Info

Publication number: WO2010118290A1
Application number: PCT/US2010/030486
Authority: WO
Inventors: Jr. Oscar D. Romero
Original assignee: Oclaro, Inc.
Priority date: 2009-04-10
Filing date: 2010-04-09
Publication date: 2010-10-14

Abstract

An optical system and method are disclosed for processing optical signals generated by a laser diode bar or other type of laser source. The method entails employing a multiple prism assembly to rearrange optical signals generated by a laser diode bar from a first spatial pattern to a second spatial pattern. The second spatial pattern may be more suited for further processing to implement particular functions. For instance, the second pattern may provide better symmetry to the optical energy generated by the laser diode bar. The second pattern may provide improved collimation of the optical signals. The second pattern may provide improved coupling of the optical energy emitted by the laser diode bar to a fiber optic cables. Other applications may take advantage of the optical signal re-arranging provided by an optical system that employs a multiple prism assembly disclosed herein.

Description

PATENT COOPERATION TREATY (PCT)

PATENT APPLICATION

FOR

STACKABLE EMITTER PRISM ASSEMBLY AND METHOD OF USE

Inventor: OSCAR D. ROMERO, JR.

Prepared by:

George L. Fountain

FOUNTAIN LAW GROUP, INC.

18201 Von Karman Ave., Suite 960

Irvine, CA 92612

Tel: (949) 769-6991

(Fax): (949) 769-6995 STACKABLE EMITTER PRISM ASSEMBLY AND METHOD OF USE

FIELD

[0001] This invention relates generally to optical systems, and in particular, to an optical system that includes a stackable emitter prim assembly and related method of use.

BACKGROUND

[0002 ] A laser diode bar is generally a high power laser formed on a semiconductor substrate. The laser diode bar typically includes a plurality of emitters arranged in a one- dimensional array. Each individual emitter comprises a p-n junction aligned substantially along the longitudinal axis of the one-dimensional array. The optical signal generated by each p-n junction diverges relatively quickly as it leaves the emitter. For example, the optical signal diverges around 10 degrees about the slow axis (e.g., the axis perpendicular to the p-n junction and on the same plane as the one- dimensional array). Along the fast axis (e.g., the axis perpendicular to the p-n junction and on a plane perpendicular to the one-dimensional array), the optical signal diverges about 40-50 degrees.

[0003] Often, it is desirable to collimate the optical signal generated by each emitter. For instance, to collimate the optical signals generated by a laser diode bar, an elongated cylindrical lens is usually disposed adjacent to and parallel with the laser diode bar. However, usually the cylindrical lens have a relatively short focal length in order to prevent optical signals from adjacent emitters to cross-couple along the slow axis. As a consequence, the optical signals may not be able to achieve the desired or optimal collimation due to the short focal length of the lens. Thus, there is a need, among others, for an optical system for improving the collimation of optical signals generated by a laser diode bar or other type of laser source. SUMMARY

[0004 ] An aspect of the invention relates to an optical system and method for processing optical signals generated by a laser diode bar or other type of laser device. The method entails employing a multiple prism assembly to rearrange optical signals generated by a laser diode bar from a first spatial pattern to a second spatial pattern. The second spatial pattern may be more suited for processing to implement particular functions. For instance, the second pattern may provide better symmetry to the optical energy generated by the laser diode bar. As an example, instead of essentially a line or one- dimensional pattern of optical signals generated by the laser diode bar, the multiple prism assembly may be configured to provide a more square or rectangular pattern of optical signals, which may be useful in many applications.

[0005] The second spatial pattern of optical signals produced by the multiple prism assembly may be configured to improve the collimation of the optical signals. For instance, it is well known that to achieve better collimation of optical signals, a lens with a relatively long focal point should be used. However, placing such lens proximate the laser diode bar may adversely result in cross-coupling of adjacent optical signals within the lens. Thus, the multiple prism assembly may be used to re-orient the optical signals from the laser diode bar along an axis perpendicular to the longitudinal axis of the laser diode bar. In this orientation, a lens with a relatively long focal point may be used to provide improved collimation, while eliminating or substantially minimizing cross- coupling of optical signals.

[0006] The improved collimation of optical signals achieved by employing the multiple prism assembly may result in better coupling of optical signals to a fiber optic cable. As previously discussed, the multiple prism assembly in conjunction with one or more lenses (e.g., a slow axis lens and a fast axis lens) may be used to achieve improved collimation of optical signals generated by a laser diode bar. The collimated optical signals may then be applied through a lens to focus the optical energy at an end of a fiber optic cable. Such processing of the optical signals, using a multiple prism assembly, collimating lenses, and focusing lens, may provide a relatively high efficient coupling of the optical energy to a fiber optic cable.

[0007 ] Other aspects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] FIG. 1 illustrates a perspective view of an exemplary prism assembly in accordance with an aspect of the disclosure.

[0009] FIG. 2 illustrates a perspective view of another exemplary prism assembly in accordance with another aspect of the disclosure.

[0010] FIG. 3 illustrates a side view of the exemplary prism assembly of

FIG. 1 in accordance with another aspect of the disclosure.

[0011] FIG. 4 illustrates a side view of a portion of the exemplary prism assembly of FIG. 1 in accordance with another aspect of the disclosure.

[0012 ] FIG. 5 illustrates a top view of the exemplary prism assembly of

FIG. 1 in accordance with another aspect of the disclosure.

[0013] FIG. 6 illustrates a top view of a portion of the exemplary prism assembly of FIG. 1 in accordance with another aspect of the disclosure.

[0014 ] FIG. 7 illustrates a perspective view of an exemplary optical system in accordance with another aspect of the disclosure.

[0015] FIG. 8 illustrates a perspective view of a first portion of the exemplary optical system of FIG. 6 in accordance with another aspect of the disclosure.

[0016] FIG. 9 illustrates a perspective view of a second portion of the exemplary optical system of FIG. 6 in accordance with another aspect of the disclosure. [0017 ] FIG. 10 illustrates a rear view of another exemplary optical system in accordance with another aspect of the disclosure.

[0018] FIG. 11 illustrates a perspective view of another exemplary optical system in accordance with another aspect of the disclosure.

[0019] FIG. 12 illustrates a side view of the exemplary optical system of

FIG. 11 in accordance with another aspect of the disclosure.

[0020] FIG. 13 illustrates a perspective view of the exemplary optical system of FIG. 11 with exemplary optical signals in accordance with another aspect of the disclosure.

[0021] FIG. 14 illustrates a side view of another exemplary optical system in accordance with another aspect of the disclosure.

[0022 ] FIG. 15 illustrates a block diagram of another exemplary optical system in accordance with another aspect of the disclosure.

[0023] FIG. 16 illustrates a block diagram of another exemplary optical system in accordance with another aspect of the disclosure.

[0024 ] FIG. 17 illustrates a block diagram of another exemplary optical system in accordance with another aspect of the disclosure.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

[0025] FIGs. 1-2 show various views of an embodiment of a stackable emitter prism assembly. As shown, the prism assembly 10 includes an assembly body 12 comprised of a first prism device 14 and at least a second prism device 16. As shown in FIG. 1, the first prism device 14 may be coupled to or otherwise secured or affixed to the second prism device 16. Optionally, the first prism device 14 need not be coupled to or in physical contact with the second prism device 16. For example, FIG. 2 shows an embodiment of the prism assembly 10 wherein the first prism device 14 is in optical communication with the second prism device 16, but not in physical contact therewith. [0026] As shown in FIGs. 3 and 4, the first prism device 14 includes a first prism body 20 defined by a first face 22, a second face 24, and a third face 26. Further, at least a portion of the first prism device 14 extends beyond the body of the second prism device 16. Similarly, at least a portion of the second prism device 16 extends beyond the body of the first prism device 14. In one embodiment the first prism body 20 is manufactured from a silica material. Optionally, the first prism body 20 may be manufactured from any variety of materials, including, without limitations, silica composite materials, composite materials, ceramics, aerogels, and the like. Further, the first prism device 14 may be formed in any variety of shapes, sizes, and/or configurations. Optionally, one or more of the faces of the first prism device 14 may include one or more optical coatings applied thereto. For example, various anti-reflective coatings, reflective coatings, wavelength-filtering coatings, holographic gratings, and the like may be deposited on the first face 22, second face 24, and/or third face 26. Optionally, the first prism device 14 may be manufactured without one or more optical coatings applied thereto.

[0027 ] FIG. 4 shows a path an incident signal would traverse through the first prism device 14. As shown, the input light beam 28A is incident on the first face 22 of the first prism device 14 and traverses through the first prism body 20. Thereafter, the light beam is reflected by the second and third faces 24, 26, respectively. In the illustrated embodiment, the light beam is reflected via total internal reflectance. Optionally, one or more coatings may be applied to the second and third faces 24, 26, respectively, to enhance reflection of the light beam. As a result, an output signal 28B is transmitted through the first face 22. In the illustrated embodiment, the input signal 28A is incident on the first face 22 at an approximately normal angle. Optionally, the input signal 28A may be incident on the first face 22 at any angle. Similarly, the output signal 28B may be transmitted through the first face 22 at any angle.

[0028] As shown in FIG. 5, the second prism device 16 includes a second prism body 30 defined by a first face 32, a second face 34, and a third face 36. In one embodiment the second prism body 30 is manufactured from a silica material. Optionally, the second prism body 30 may be manufactured from any variety of materials, including, without limitations, silica composite materials, composite materials, ceramics, aerogels, and the like. In one embodiment, the first and second prism devices 14, 16 may be manufactured from the same material. In an alternate embodiment, the first and second prism devices 14, 16 may be manufactured from different materials. Further, the second prism device 16 may be formed in any variety of shapes, sizes, and/or configurations. Optionally, one or more of the faces of the second prism device 16 may include one or more optical coatings applied thereto. For example, various anti-reflective coatings, reflective coatings, wavelength-filtering coatings, holographic gratings, and the like may be deposited on the first face 32, second face 34, and/or third face 36. Optionally, the second prism device 16 may be manufactured without one or more optical coatings applied thereto. Further, as shown in Fig. 5, at least a portion of the first face 32 of the second prism body 30 extends beyond the first prism device 14.

[0029] FIG. 6 shows a path an incident signal would traverse through the second prism device 16. As shown, the input light beam 38A is incident on the first face 32 of the second prism device 16 and traverses through the second prism body 30. Thereafter, the light beam is reflected by the second and third faces 34, 36, respectively, through total internal reflectance. Optionally, one or more optical coatings may be applied to the second and third faces 34, 36 to enhance reflectance of the optical signal. As a result, an output signal 38B is transmitted through the first face 32. In the illustrated embodiment, the input signal 38A is incident on the first face 32 at an approximately normal angle (i.e. perpendicular to the first face 32). Optionally, the input signal 38A may be incident on the first face 32 at any angle. Similarly, the output signal 38B may be transmitted through the first face 32 at any angle.

[0030] FIGs. 7-9 show various views of an embodiment of a prism assembly

10 during use. As shown, the prism assembly 10 is positioned to receive one or more light signals from a diode bar assembly 40. In the illustrate embodiments, the diode bar assembly 40 includes multiple diode emitters 42A-42D. Those skilled in the art will appreciate that the diode bar assembly 40 may include any number of diode emitters positioned thereon, each emitter configured to output one or more light beams. In the illustrated embodiment, the first emitter 42A outputs a first output signal 44A, and the second emitter 42B outputs a second output signal 44B. Similarly, the third emitter 42 C outputs a third output signal 44C and the fourth emitter 42D outputs a fourth output signal 44D. As shown, the diode bar assembly 40 emits the output signals 44A-44D in a first signal orientation 46.

[0031] Referring again to FIGs. 4 and 6-9, the third and fourth output signals 44C, 44D are not incident on the prism assembly 10. In contrast, the first and second output signals 44A, 44B are incident on prism assembly 10. As shown, the first and second output signals 44A, 44B propagate through the first face 22, of the first prism device 14, and are reflected to the third face 26 of the first prism device 14 by the second face 24. Thereafter, the third face 26 directs the first and second signals 44A, 44B though the first face 22 of the first prism device 14 to the first face 32 of the second prism device 16 positioned proximate to the first prism device 14. In the illustrated embodiment, the first prism assembly 14 alters the vertical position of the first and second output signals 44A, 44B relative to the third and fourth output signals 44C, 44D. The first and second signals 44A, 44B are reflected by the second and third faces 34, 36, respectively, of the second prism device 16 and emerge from the prism assembly 10 proximate to the third and fourth output signals 44C, 44D. In the illustrated embodiment, the second prism assembly 16 alters the horizontal position of the first and second output signals 44A, 44B relative to the third and fourth output signals 44C, 44D. FIGs. 7-9 show the position of the re-oriented first and second output signals 48A, 48B positioned proximate to the third and fourth output signals 44C, 44D. As shown, the output of the diode bar assembly 46 has been modified by the prism assembly 10 to produce a re-oriented output profile 50.

[0032 ] In the illustrated embodiments, a single prism assembly 10 comprises a first prism device 14 and a second prism assembly 16. Optionally, the prism assembly 10 may be comprised of multiple first prism devices 14 and second prism devices 16. FIG. 10 shows an assembly body 12 comprised of four first prism devices 14A-14D optically coupled to four second prism devices 16A- 16D. During use, a first optical signal 18A-1 received from a diode bar device or other optical signal source (not shown) is incident on the first prism device 14 A, which directs the signal to the second prism device 16A. Thereafter, the optical signal is outputted by the second prism device 16A. Adjacent optical signals 18A-2 to 18A- 4 are similarly reconfigured by adjacent prism assemblies (14B, 16B), (14C, 16C), and (14D, 16D) to form output signals 18B-2 to 18B-4, respectively. As a result, the generally horizontally distributed output 18A-0 to 18A- 4 of the optical signal source may be easily reconfigured to a generally vertically distributed output 18A-0 and 18B- 1 to 18B-4 to by the prism assembly 10.

[0033] FIGs. 11 and 12 show an alternate embodiment of a prism assembly

110. As shown, the prism assembly 110 includes an assembly body 112 having a first prism device 114 and at least a second prism device 116 coupled to or otherwise secured to a substrate body 118. In one embodiment, the substrate body 118 is configured to permit an optical signal to propagate therethrough. For example, in one embodiment, the substrate body 118 is manufactured from Silica glass. Like the previous embodiments, the first prism device 114, second prism device 116, and/or the substrate body 118 may be manufactured in any variety of sizes, shapes, angles, thicknesses, and from any variety of materials. Optionally, the first prism device 114, second prism device 116, and/or the substrate body 118 may include one or more optical coatings applied thereto. Exemplary coatings include, for example, antireflection coatings, reflective coatings, wavelength-filtering coatings, and the like.

[0034 ] FIG. 13 shows the embodiment of the prism assembly 110 shown in

FIGs. 11 and 12 during use. As shown, the optical signals 120C and 120D are emitted from a diode bar device or other optical signal source (not shown) and propagate through the substrate body 118. In contrast, the optical signals 120A and 120B are transmitted through the substrate body 118 and are reflected into the second prism device 116 by the first prism device 114 as detailed in paragraph [0007] above, thereby altering the vertical position of the optical signals 120A, 120B relative to the optical signals 120C, 120D. Thereafter, the optical signals 120A, 120B are reflected by the faces of the second prism device 116, resulting in the optical signals 120A, 120B are positioned proximate to the optical signals 120C, 120D. As a result, the generally linear output of a diode bar device (not shown) may be reconfigured by the prism assembly 110 to produce the stacked output profile 122.

[0035] As shown in Fig. 14, a multiple prism assembly 150 may include a plurality of cascaded prism sub-assemblies. A first prism sub-assembly may include a substrate 112, a first vertical-repositioning prism 114-1, and a first horizontal-repositioning prism 116-1. A second prism sub-assembly may include a second vertical-repositioning prism 114-2, and a second horizontal- repositioning prism 116-2. Similarly, a third prism sub-assembly may include a third vertical-repositioning prism 114-3, and a third horizontal-repositioning prism 116-3. The prism sub assemblies may be cascaded to successively shift vertical and horizontally optical signals in order to re-arrange optical signals generated by a laser diode bar 160 from a generally horizontal orientation to a vertical orientation 124, as shown.

[0036] In general, in the next set of examples, optical systems are described as having a multiple prism assembly rearrange a first spatial pattern of optical signals received from an optical signal source into a second spatial pattern of optical signals. The second pattern of optical signals is more useful in different applications. For example, in one application, the multiple prism assembly is used to improve the collimation of optical signals generated by a laser diode bar. In a second application, the multiple prism assembly operates on a portion of the optical signals generated by a laser diode bar to improve symmetry of the optical signals. In a third application, the multiple prism assembly may be used in conjunction with one or more lenses to improve the coupling of optical signals from a laser diode bar to a fiber optic cable. These applications are merely examples, and many others are realizable using the concepts described herein.

[0037 ] FIG. 15 illustrates a block diagram of another exemplary optical system 200 in accordance with another aspect of the disclosure. In summary, the optical system 200 employs a multiple prism assembly to improve the collimation of optical signals generated by an optical signal source. More specifically, the optical system 200 comprises an optical signal source 202, a multiple prism assembly 204, and one or more lenses 206.

[0038] The optical signal source 202 may be a laser diode bar or other type of laser that produces a plurality of optical signals arranged in a first pattern. For instance, in the case of a laser diode bar, the optical signals are arranged in a one-dimensional array extending along the slow axis of emission. The multiple prism assembly 204 operates on at least a portion of the output signals from the source 202 to rearrange the optical signals for improved collimation by the one or more lenses 206. The one or more lenses 206 collimate the optical signals from the multiple prism assembly 204 and/or directly from the optical signal source 202. For instance, the one or more lenses may include a first lens to collimate the optical signals along the fast axis, and a second lens to collimate the optical signals along the slow axis.

[0039] As discussed in the Background section herein, it is desirable to use a lens with a relatively long focal point to better collimate the optical signals from a laser diode bar. However, placing such lens immediately in front of a laser diode bar would adversely result in the cross-coupling of adjacent optical signals. To solve this problem, the multiple prism assembly 204 is situated between the laser diode bar 202 and the collimating lens 206 to re-arrange the optical signals along the slow axis (e.g., horizontal axis) to the fast axis (e.g., vertical axis), and sufficiently space the optical signals apart such that cross- coupling of adjacent light within the collimating lens 206 is substantially eliminated. Thus, in this optical system 200, using the multiple prism assembly 204, improved collimated optical signals may be achieved.

[0040] FIG. 16 illustrates a block diagram of another exemplary optical system 220 in accordance with another aspect of the disclosure. In summary, the optical system 220 includes a multiple prism assembly configured to re-arrange a portion of the optical signals generated by an optical signal source to improve the symmetry arrangement of the optical signals. In particular, the optical system 220 comprises an optical signal source 222 and a multiple prism assembly 224. [0041] The optical signal source 222 may be a laser diode bar or other type of laser that produces a plurality of optical signals arranged in a first pattern. For instance, in the case of a laser diode bar, the optical signals are arranged in a one-dimensional array extending along the slow axis of emission. The multiple prism assembly 204 operates on a portion of the output signals from the source 202 to rearrange the optical signals for improved symmetry of the optical signals. For example, the optical signals from a laser diode bar 222 may be spaced substantially linear along the slow axis of emission. To improve symmetry, the multiple prism assembly 224 may be adapted to operate on half the optical signals to stack them with respect to the other half along the fast axis (e.g., to vertically stack the halves).

[0042 ] FIG. 17 illustrates a block diagram of another exemplary optical system 250 in accordance with another aspect of the disclosure. In summary, the optical system 250 includes a multiple prism assembly and one or more lenses to provide an efficient coupling of the optical signals generated by an optical signal source to a fiber optic cable. In particular, the optical system 250 comprises an optical signal source 252, a multiple prism assembly 254, one or more lenses 256, and a fiber optic cable 258.

[0043] The optical signal source 252 may be a laser diode bar or other type of laser that produces a plurality of optical signals arranged in a first pattern. For instance, in the case of a laser diode bar, the optical signals are arranged in a one-dimensional array extending along the slow axis of emission. The multiple prism assembly 254 operates on at least a portion of the output signals from the source 252 to rearrange the optical signals for improved collimation by the one or more lenses 256. The one or more lenses 256 collimate the optical signals from the multiple prism assembly 254 and/or directly from the optical signal source 252. For instance, the one or more lenses 256 may include a first lens to collimate the optical signals along the fast axis, and a second lens to collimate the optical signals along the slow axis. Additionally, the one or more lenses 256 may include an additional lens to focus the collimated optical signals to an end of the fiber optic cable 258 to improve the coupling of the optical signals to the cable. [0044 ] While the invention has been described in connection with various embodiments, it will be understood that the invention is capable of further modifications. This application is intended to cover any variations, uses or adaptation of the invention following, in general, the principles of the invention, and including such departures from the present disclosure as come within the known and customary practice within the art to which the invention pertains.

Claims

What is claimed is:

1. An optical system, comprising: an optical signal source adapted to generate a plurality of optical signals arranged in a first spatial pattern; and a multiple prism assembly adapted to spatially rearrange at least a portion of the optical signals from the first spatial pattern to a second spatial pattern.

2. The optical system of claim 1, wherein the optical signal source comprises a laser diode bar.

3. The optical system of claim 2, wherein the first spatial pattern of optical signals generated by the laser diode bar comprises substantially a first one-dimensional pattern of optical signals spaced apart along a slow axis.

4. The optical system of claim 3, wherein the second spatial pattern of optical signals produced by the multiple prism assembly comprises substantially a second one- dimensional pattern of optical signals spaced apart along a fast axis.

5. The optical system of claim 4, further comprising one or more lenses adapted to modify at least a portion of the optical signals arranged in the second one-dimensional pattern.

6. The optical system of claim 5, wherein the one or more lenses are adapted to collimate at least the portion of the optical signals arranged in the second one- dimensional pattern.

7. The optical system of claim 6, wherein the one or more lenses comprises: a first lens adapted to collimate at least the portion of the optical signals arranged in the second one- dimensional pattern along the slow axis; and a second lens adapted to collimate at least the portion of the optical signals arranged in the second one- dimensional pattern along the fast axis.

8. The optical system of claim 7, further comprising a fiber optic cable.

9. The optical system of claim 8, wherein the one or more lenses further comprises a lens adapted to focus the collimated optical signals at an end of the fiber optic cable.

10. The optical system of claim 1, wherein the first spatial pattern of optical signals comprises a one- dimensional pattern of optical signals spaced apart along a longitudinal axis.

11. The optical system of claim 10, wherein the multiple prism assembly comprises a first prism adapted to shift at least a portion of the optical signals in a direction substantially perpendicular to the longitudinal axis.

12. The optical system of claim 11, wherein the multiple prism assembly comprises a second prism adapted to shift the at least portion of the optical signals shifted by the first prism in a direction substantially parallel with the longitudinal axis.

13. The optical system of claim 12, wherein the first and second prism make physical contact with each other.

14. The optical system of claim 12, wherein the first and second prism do not make physical contact with each other.

15. The optical system of claim 1, wherein the multi prism assembly comprises a substrate through which at least a portion of the optical signals propagate.

16. An method of processing optical signals, comprising: generating a plurality of optical signals arranged in a first spatial pattern; and applying at least a portion of the optical system through a multiple prism assembly to spatially rearrange the optical signals from the first spatial pattern to a second spatial pattern.

17. The method of claim 16, wherein generating the optical signals comprises activating a laser diode bar to generate the optical signals.

18. The method of claim 17, wherein the first spatial pattern of optical signals comprises substantially a first one-dimensional pattern of optical signals spaced apart along a slow axis.

19. The method of claim 18, wherein the second spatial pattern of optical signals comprises substantially a second one- dimensional pattern of optical signals spaced apart along a fast axis.

20. The method of claim 19, further comprising applying at least a portion of the optical signals arranged in the second one-dimensional pattern through one or more lenses.

21. The method of claim 19, further comprising collimating at least a portion of the optical signals arranged in the second one- dimensional pattern.

22. The method of claim 21, wherein collimating comprises: collimating at least a portion of the optical signals arranged in the second one-dimensional pattern along the slow axis; and collimating at least a portion of the optical signals arranged in the second one-dimensional pattern along the fast axis.

23. The method of claim 21, applying the collimated optical signals to a fiber optic cable.

24. The method of claim 23, wherein applying the collimated optical signals to a fiber optic cable comprises focusing the collimated optical signals at an end of the fiber optic cable.

25. The method of claim 16, wherein the first spatial pattern of optical signals comprises a one- dimensional pattern of optical signals spaced apart along a longitudinal axis.

26. The method of claim 25, wherein applying the optical signals through the multiple prism assembly comprises shifting at least a portion of the optical signals in a direction substantially perpendicular to the longitudinal axis.

27. The method of claim 26, wherein applying the optical signals through the multiple prism assembly comprises shifting the at least portion of the optical signals shifted in the longitudinal axis in a direction substantially parallel with the longitudinal axis.