WO2001084201A2

WO2001084201A2 - Low loss ultra stable fabry-perot etalon

Info

Publication number: WO2001084201A2
Application number: PCT/US2001/013867
Authority: WO
Inventors: Gan Zhou; Kuang-Yi Wu; Leo Yu-Yu Lin; Charles S. I. Wong; Sihan Lin
Original assignee: Chorum Technologies Lp
Priority date: 2000-05-01
Filing date: 2001-04-30
Publication date: 2001-11-08
Also published as: AU2001261090A1; WO2001084201A3

Abstract

A low loss stable Fabry-Perot etalon is disclosed. In the preferred embodiment the Fabry-Perot etalon comprises a housing made of a material with a low coefficient of thermal expansion, an optical fiber connected to the housing for providing an optical signal and a reflecting surface preferably being part of the housing for receiving the optical signal from the optical fiber. In the preferred embodiment, the reflecting surface reflects the received optical signal substantially back to the optical fiber. If desired, a tuning plate may be positioned in a cavity between the reflecting surface and the optical fiber. The tuning plate may be used for tuning the cavity between the reflecting surface and the optical fiber to a desired wavelength.

Description

LOW LOSS ULTRA STABLE FABRY-PEROT ETALON

RELATED APPLICATIONS

The present application claims the benefit of co-pending U.S. Provisional Patent Application No. 60/200,969, entitled "LOW LOSS ULTRA STABLE FABRY-PEROT ETALON," filed May 1, 2000, the disclosure of which is incorporated herein by reference. The present application is related to concurrently filed U.S. Patent Application [Attorney Docket No. 55872-P054US-10001290], entitled "OPTICAL DEVICE HAVING POLARIZATION ELEMENTS," the disclosure of which is incorporated herein by reference.

TECHNICAL FIELD

The present invention relates generally to optical systems and elements and in particular to a low loss ultra stable Fabry-Perot etalon.

BACKGROUND

An etalon is typically used as a frequency or wavelength filter in optical signals, such as may be used in an optical communications network. In the communications industry, an etalon can be used to select different channels that can be broadcast on an optic fiber. By tuning the etalon to different wavelengths, different channels can be set up. However, the stability of prior art etalons is dependent on the change of the index of refraction of the material forming the etalon with temperature and also the change in the dimension of the material with temperature. Furthermore, when a coupler is used to feed the optical signal from a fiber into the core of another fiber, there would usually be a coupling loss as all the energy from the source fiber would not be picked up by the destination fiber. Moreover, it is difficult to tune prior art etalon devices to the desired wavelength or frequency. Typically, a piezoelectric device may be used to apply stress to a fiber of the etalon in order to tune the etalon. In the alternative, a prior art etalon can be tuned by enclosing the etalon in a temperature controlled housing and then adjusting the temperature in the housing to tune the transmission curve of the etalon. Thus, prior art etalons suffer from the problems of coupling losses and are also unstable due to the index of refraction of the material of the etalon and/or the dimension of the etalon being dependent on the change of temperature.

Therefore, there is a need in the art for a stable etalon with a low coupling loss.

SUMMARY OF THE INVENTION

These and other objects, features and technical advantages are achieved by a Fabry- Perot etalon, wherein a preferred embodiment Fabry-Perot etalon comprises a housing made of a material with a low coefficient of thermal expansion, an optical fiber connected to the housing for providing an optical signal and a reflecting surface preferably being part of the housing for receiving the optical signal from the optical fiber. In the preferred embodiment, the reflecting surface reflects the received optical signal substantially back to the optical fiber.

If desired, a tuner, such as a tuning plate, may be positioned in a cavity between the reflecting surface and the optical fiber. The tuning plate may be used for tuning the cavity between the reflecting surface and the optical fiber to a desired wavelength. In the preferred embodiment, the tuning plate is a very thin parallel plate that allows substantial tuning without substantial change in the wavelength.

The housing of the preferred embodiment is made of a material with a low coefficient of thermal expansion. Thus, the size of the cavity does not change substantially with a change in temperature, thereby providing a more stable etalon.

The preferred embodiment etalon has a low insertion loss because the reflecting surface reflects substantially the entire received optical signal from the optical fiber back to the optical fiber. The cavity between the reflecting surface and the optical fiber is an air cavity and the index of refraction of air does not change significantly with temperature. Thus, the problems associated with the change in refractive index of the material of the etalon due to change in temperature are not present in the etalon of the preferred embodiment because there is no material in the cavity between the reflecting surface and the optical fiber. Accordingly, the preferred embodiment etalon is highly stable. Furthermore, in the preferred embodiment etalon, the optical fiber may be coupled to the housing directly without the need to use collimating optics.

Accordingly, it is a technical advantage of a preferred embodiment of the present invention to provide an etalon made of a material having a low coefficient of thermal expansion. It is another technical advantage of a preferred embodiment of the present invention to provide an etalon with a tunable cavity.

It is a further technical advantage of a preferred embodiment of the present invention to provide an etalon with a tunable cavity with very low sensitivity to tuning position or angle.

It is a further technical advantage of a preferred embodiment of the present invention to provide an etalon with a very low insertion loss.

It is yet another technical advantage of a preferred embodiment of the present invention to provide an etalon with a very high coupling efficiency. It is yet another technical advantage of a preferred embodiment of the present invention to provide an etalon wherein the alignment of the etalon is insensitive to the tuning plate position or orientation.

The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.

BRIEF DESCRIPTION OF THE DRAWING

For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawing, in which:

FIGURE 1 is a pictorial representation of a prior art Fabry-Perot etalon; FIGURE 2 is a pictorial representation of another prior art Fabry-Perot etalon;

FIGURE 3 is a pictorial representation of another prior art Fabry-Perot etalon;

FIGURES 4A and 4B are pictorial representations of alternative embodiments of the prior art etalon of FIGURE 2;

FIGURE 5 is a pictorial representation of a preferred embodiment Fabry-Perot etalon of the present invention; .

FIGURE 6 shows the operation of a tuning plate of the preferred embodiment;

FIGURES 7A and 7B are pictorial representations of an alternative embodiment Fabry-Perot etalon of the present invention;

FIGURE 8 is a schematic of an interferometric wavelength router utilizing the preferred embodiment Fabry-Perot etalon of the present invention; and

FIGURE 9 is a schematic of a system utilizing the alternative embodiment Fabry- Perot etalon of the present invention.

DETAILED DESCRIPTION

In order to better understand the present invention and its associated advantages, different embodiments of prior art Fabry-Perot etalons are described with reference to FIGURES 1-4.

FIGURE 1 is a pictorial representation of a prior art Fabry-Perot etalon 10. Etalon 10 is made of a solid block of material which is cut and polished on two parallel surfaces and coated on opposing surfaces. The stability of etalon 10 depends on the change of the index of refraction of the material forming the etalon with temperature. The stability of etalon 10 also depends on the change in the dimension of the material of the etalon with temperature, i.e. the coefficient of thermal expansion of the material of etalon 10. If the etalon is not stable as the temperature changes, then the optic filter waveform of the optic signal provided to the etalon may also change, i.e. it drifts along the frequency axis. Thus, a particular channel of signal that was detectable at a particular temperature would not be detectable at a different temperature due to this drift. Consequently, a pass channel could become a channel that would be stopped and vice versa, thereby causing loss of the chamiel signal. Furthermore, etalon 10 of FIGURE 1 does not include a suitable mechanism to tune the etalon, which makes it difficult to match to a particular wavelength.

FIGURE 2 is a pictorial representation of another prior art Fabry-Perot etalon 20. Etalon 20 is an air gap etalon implemented by placing two optic fibers 21 and 22 close together with a gap 23 between the two fibers. Because of the gap 23 between the two fibers, etalon 20 is less susceptible to instability due to a change in index due to change in temperature and consequently has a low drift. However, because of the gap 23 between the two fibers 21 and 22, there is a high coupling or insertion loss in energy in the etalon of FIGURE 2. This is because in single mode fibers as light comes out of a first fiber, it diverges and a second fiber attempting to pick up the light dispersed from the first fiber without the use of any lens or other optics elements is able to pick up only a portion of the dispersed light. Thus, there is a high insertion loss in the etalon of FIGURE 2.

FIGURE 3 is a pictorial representation of another prior art Fabry-Perot etalon 30. Etalon 30 is formed by coating two opposing ends of a solid fiber. Thus, it has the same problems of high drift of the filter waveform as the etalon shown in FIGURE 1. Moreover, etalon 30 of FIGURE 3 is also difficult to tune to the desired frequency or wavelength. Typically a piezoelectric device is used to apply stress on the fiber in order to properly tune etalon 30 to the right frequency or wavelength.

FIGURES 4A and 4B are pictorial representations of alternative embodiments of the etalon of FIGURE 2. Etalon 40 of FIGURE 4A is an air gap etalon implemented by placing two optic fibers 41 and 42 close together. A solid block of fiber 44 is placed in a gap 43 between fibers 41 and 42. In the embodiment of FIGURE 4A, one side of fiber 44 is coupled to optic fiber 41, whereas there is a gap between fiber 42 and the other side of fiber 44. Thus, etalon 40 can be tuned from one side. The presence of fiber 44 in gap 43 reduces the amount of insertion loss that is inherent in the etalon of FIGURE 2 as the cavity between the two fibers 41 and 42 is reduced. However, the presence of the fiber in the gap causes similar problems as those caused in the etalon of FIGURE 1 due to the change in the refractive index and dimension of the material of the fiber due to a change in temperature. Etalon 40' of FIGURE 4B is another alternative embodiment of the etalon of

FIGURE 2. Etalon 40' is an air gap etalon implemented by placing two optic fibers 41' and 42' close together. A solid block of fiber 44' is placed in a gap between fibers 41' and 42'. In the embodiment of FIGURE 4B, fiber 44' is not coupled to any of the fibers 41' or 42'. Thus, there is a gap 43' between fiber 42' and one side of fiber 44' and a gap 45' between fiber 41 ' and the other side of fiber 44'. Thus, etalon 40' can be tuned from both sides. The presence of fiber 44' in between fibers 41' and 42' reduces the amount of insertion loss that is inherent in the etalon of FIGURE 2 as the cavity between the two fibers 41' and 42' is reduced. However, the presence of the block of fiber in between fibers 41' and 42' causes similar problems of high drift as those caused in the etalon of FIGURE 1 due to the change in the index of refraction and dimension of the material of the fiber due to a change in temperature.

FIGURE 5 is a pictorial representation of a preferred embodiment Fabry-Perot etalon (FP etalon) of the present invention. FP etalon 50 of FIGURE 5 comprises a housing 51. A plano-concave reflecting mirror 53 is positioned on one side of etalon 50 with the concave surface of reflecting mirror 53 preferably facing towards the interior of the etalon. The mirror is preferably formed of a material having a low coefficient of thermal expansion. In the preferred embodiment, the mirror is made of zerodur. In alternative embodiments, other substances, such as glass, fused silica, or the like may also be used. The concave surface of the mirror is preferably coated with a reflective coating, such as a multi-layer dielectric coating. In the preferred embodiment, the reflectivity of the reflective coating is in the range of 90% to 100% and preferably approximately 100%.

Housing 51 has a hole or a bore on the side of the housing which is opposite the piano concave mirror 53. Housing 51 is preferably made of zerodur. An optical fiber 52 is coupled to the bore. Thus, the optical fiber and mirror are separated by an air cavity 54. In the preferred embodiment, fiber 52 is a single mode fiber. Preferably, the core of fiber 52 expands or tapers such that the core is wider at the end facing the plano-concave mirror 53 ("the mirror end") and narrower at the end facing away from the plano-concave mirror . In alternative embodiments, the core of fiber 52 could be of uniform width, if desired. The mirror end of fiber 52 is preferably polished to be optically flat and coated with a reflective coating, such as a multi-layered dielectric coating. In the preferred embodiment, the reflectivity of the coating is approximately 10% to 30% . Preferably the reflectivity of the coating is approximately 20%.

When the numerical aperture of the light beam from fiber 52 is low, for example 0.1 or lower, such as in the case of the preferred embodiment tapered core fiber, the radius of curvature of the concave surface of mirror 53 is preferably uniform. However, when the numerical aperture of the light from fiber 52 is high, such as 0.3 or higher, the radius of curvature of the concave surface of mirror 53 is not uniform, i.e. it is slightly aspherical, to compensate for spherical aberrations.

In the preferred embodiment, the mirror end of fiber 52 is positioned at the focal point of the plano-concave mirror 53, i.e. the distance of the mirror end of fiber 52 from the concave surface is approximately equal to twice the focal length of the mirror. Thus, substantially all the light coming out of the mirror end of fiber 52 is reflected back into the fiber. Accordingly, substantially all of the light from the fiber is collected back into the fiber. Subsequently, the etalon of the preferred embodiment of FIGURE 5 has a very low insertion loss. Moreover, because of the air gap 54 between fiber 52 and mirror 53, there is very little temperature drift. As there is only very small change of the index of refraction of air with temperature and the plano-concave mirror is preferably made of zerodur which has a very low coefficient of thermal expansion, the etalon of the preferred embodiment is highly stable.

Thus, in the preferred embodiment implementation of FIGURE 5, an optical fiber can be coupled directly to a resonator without having to use collimating optics. As shown in FIGURE 5, the piano concave mirror reflects the diverging light from the fiber back into the fiber. Thus, the system has a very low (if any) coupling loss. A tuning plate (not shown) could be inserted in the cavity 54. The tuning plate is preferably made of a material with a low coefficient of thermal expansion, such as fused silica. In alternative embodiments, the tuning plate may be made of a material, such as zerodur, glass, ULE, pyrex, BK7 and/or the like. The principle of operation of the tuning plate is shown in FIGURE 6. A beam of light 61 incident on a first surface 62 of tuning plate 60 is refracted inside the tuning plate. Once the refracted light 64 hits the second surface 63, it comes out of tuning plate 60 as beam 65 and is substantially parallel to the incident beam 61. Thus, by passing through tuning plate 60, the beam of light undergoes an increase in path length as it travels through the angled tuning plate.

The center wavelength of cavity 54 may be selected by selecting the angle of the tuning plate. Tuning of the cavity is accomplished by changing the overall optical path length. Thus, by changing the angle of the plates, the amount of travel of the light within the plate changes thereby increasing the overall optical path length. By turning the tuning plate to a desired angle, the center wavelength of the cavity could be matched to a specified wavelength, such as a wavelength specified by a standard body, for example the International Telecommunications Union. Accordingly, the center wavelength of the etalon could be tuned very well.

In the preferred embodiment, the tuning plate is very thin, for example approximately 100 μm. In alternative embodiments the thickness of the tuning plate may be in the range of 20 μm to 200 μm. The thin material of the tuning plate makes the cavity center wavelengths insensitive to temperature changes in the environment. This is because the change in path length caused by the change in the index of the thin tuning plate due to a change in temperature is very small relative to the entire path length.

FIGURES 7A and 7B are pictorial representations of an alternative embodiment Fabry-Perot etalon of the present invention. Fabry-Perot etalon 70 of FIGURES 7 A and 7B comprises a housing 71. A plano-plano reflecting mirror 72 is positioned on one side of etalon 70. The mirror is preferably formed of a material having a low coefficient of thermal expansion. In the preferred embodiment, the mirror is made of zerodur. In alternative embodiments, other substances, such as glass, fused silica, or the like may also be used. The surface of the mirror facing the interior of the etalon is preferably coated with a reflective coating, such as a multi-layer dielectric coating. In the preferred embodiment, the reflectivity of the reflective coating is in the range of 90% to 100% and preferably approximately 100%.

In the embodiment of FIGURES 7A and 7B, a second plano-plano reflecting mirror 73 is preferably positioned on the side of housing 71 opposite the reflecting mirror 72. The surface of mirror 73 facing the mirror 72 is preferably partially coated with a reflective coating, such as a multi-layer dielectric coating. In the preferred embodiment, the reflectivity of the coated portion of the mirror is approximately 100%. In alternative embodiments, the reflectivity of mirror 73 may be as low as 20% depending on the application. For example, when inco orating etalon 70 of FIGURES 7 A and 7B into an interferometric wavelength router, such as shown in FIGURE 8, mirror 73 may be coated to be partially reflecting, while mirror 72 may be coated to be substantially reflecting.

The length of cavity 75 between the two mirrors may be adjusted by changing the distance between the two mirrors. Once the desired cavity length is achieved the positions of the two mirrors may be fixed by fixing the mirrors to the housing, for example by using a thermosetting resin, such as epoxy, or any other suitable adhesive.

Preferably a thin tuning plate 74 is inserted in cavity 75. Tuning plate 74 is preferably made of a material with a low coefficient of thermal expansion, such as fused silica. In alternative embodiments, the tuning plate may be made of a material, such as zerodur, ULE, pyrex, BK7, and or the like. The center wavelength of cavity 75 may be selected by selecting the angle of the tuning plate 74. Tuning of the cavity is preferably accomplished by changing the overall optical path length. Thus, by changing the angle of the plate, the amount of travel of the light within the plate changes thereby increasing the overall optical path length.

In the preferred embodiment, the tuning plate is very thin, for example approximately 100 μm. In alternative embodiments the thickness of the tuning plate may be in the range of 20 μm to 200 μm. The thin material of the tuning plate makes the cavity center wavelengths insensitive to temperature changes in the environment. This is because the change in path length caused by the change in the index of the thin tuning plate due to a change in temperature is very small relative to the entire path length. The FP etalon of FIGURES 7 A and 7B is designed for operation with a plain wave incident beam. Thus, for the plano-plano FP etalon of FIGURES 7A and 7B, the optical signal or beam out of an optical fiber is preferably collimated and then provided to a wavelength routing device. Thus, as shown in the system 90 of FIGURE 9, an optical signal from optical fiber 91 is provided to a collimating lens 92. Collimating lens 92 provides a collimated signal preferably to FP etalon 93.

The collimated signal from collimating lens 92 is provided to etalon 73 of

FIGURES 7 A and 7B or etalon 93 of FIGURE 9 is passed through mirror 73 and falls on mirror 72. In the preferred embodiment, the collimated beam is reflected multiple times within cavity 75 by the two mirrors 72 and 73. The beam is then reflected back from the etalon onto the optical fiber 91.

On the other hand, the piano concave FP etalon of FIGURE 5 is preferably used with a system where an optical beam or signal from the optical fiber is directly coupled to a wavelength router and there is no collimating optics between the fiber and the mirror. This particular configuration can be used, for example, in a wavelength implementation of a Michelson GTR interferometer for wavelength routing.

The etalon of the present invention provides several advantages. The presence of the air gap or cavity reduces the drift of the wavelength. There is a very small change in the refractive index of air with temperature. Accordingly, the drift in the optic filter waveform due to a temperature change is low. Moreover, the presence of the air gap eliminates or reduces the dimensional effect caused by change in temperature of the material of the fiber. Thus, the etalon is more stable.

Moreover, the presence of the tuning plate allows tuning of the cavity of the etalon. Furthermore, the alignment of the FP etalon is insensitive to fine tuning the plate position or orientation since the thin tuning plates add only a negligible amount of distortion to the optical wavefront. Thus, the device is robust. In the preferred embodiment, the residual change in frequency due to a temperature change of the tuning plate is less than 0.1 GHz/°C.

FIGURE 8 is a schematic of an interferometric wavelength router 80 utilizing the preferred embodiment Fabry-Perot etalon of the present invention. Interferometer 80 comprises a circulator 82, a coupler 84, and a FP etalon 85. In FIGURE 8, optical signal from fiber 81 is provided as an input to circulator 82. Circulator 82 ensures that optical signals entering circulator 82 from fiber 81 flows out through fiber 89 to coupler 84. Coupler 84 may also receive optical signals from other fibers, such as fiber 87. These signals are fed to fiber 86 which provides the signal to FP etalon 85 of the present invention. FP etalon 85 reflects the beam and transmits it back over fiber 86. As discussed above, FP etalon 85 is stable and has a low insertion loss. Signal from etalon 85 passes through fiber 86 and is fed to coupler 84. Coupler 84 is capable of receiving signals from other fibers, such as fiber 88. The signals from fibers 86 and 88 are fed to fibers 89 and 87. Signal from fiber 89 passes through circulator 82 to fiber 83.

Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.

Claims

WHAT IS CLAIMED IS:

1. A stable Fabry-Perot etalon, comprising: a housing made of a material with a low coefficient of thermal expansion; an optical fiber connected to said housing for providing an optical signal; and a reflecting surface being part of said housing for receiving said optical signal from said optical fiber, wherein said surface reflects said received optical signal substantially back to said optical fiber.

2. The Fabry-Perot etalon of claim 1, wherein said reflecting surface is a concave reflecting surface.

3. The Fabry-Perot etalon of claim 2, wherein said concave reflecting surface is part of a plano-concave mirror.

4. The Fabry-Perot etalon of claim 3, wherein said plano-concave mirror is formed of a material having a low coefficient of thermal expansion.

5. The Fabry-Perot etalon of claim 1, wherein said reflecting surface has a reflectivity of approximately 100%).

6. The Fabry-Perot etalon of claim 3, wherein an end of said optical fiber is positioned at a confocal point of said plano-concave mirror, wherein said positioning of said end of said optical fiber facilitates said substantial reflection of said received optical signal back to said optical fiber.

7. The Fabry-Perot etalon of claim 2, wherein said concave reflecting surface has a substantially uniform radius of curvature.

8. The Fabry-Perot etalon of claim 1, further comprising: a tuner for tuning a cavity between said reflecting surface and said optical fiber to a desired wavelength.

9. The Fabry-Perot etalon of claim 8, wherein an angle of said tuner in said cavity determines a center wavelength of said cavity.

10. The Fabry-Perot etalon of claim 8, wherein said tuner is a tuning plate of thickness approximately 100 μm.

11. The Fabry-Perot etalon of claim 8, wherein said tuner is a tuning plate of thickness in the range between 20 μm and 100 μm.

12. The Fabry-Perot etalon of claim 8, wherein said tuner is made of a material having a low thermal expansion coefficient.

13. The Fabry-Perot etalon of claim 8, wherein said tuner is made of a material comprising fused silica.

14. The Fabry-Perot etalon of claim 8, wherein said tuner is made of a substance comprising a material selected from the group consisting of zerodur, glass, BK7, pyrex, and ULE.

15. The Fabry-Perot etalon of claim 1, wherein said optical fiber is a single mode fiber.

16. The Fabry-Perot etalon of claim 1 , wherein a core of said optical fiber is tapered from one end to an opposite end, wherein the end facing the concave reflecting surface is wider than the other end.

17. The Fabry-Perot etalon of claim 1, wherein a core of said optical fiber is of uniform width.

18. The Fabry-Perot etalon of claim 1, wherein an end of said optical fiber facing said concave reflecting surface is coated with a reflective coating.

19. The Fabry-Perot etalon of claim 18, wherein said reflective coating has a reflectivity of approximately 20%.

20. The Fabry-Perot etalon of claim 18, wherein said reflective coating has a reflectivity in the range of approximately 10% to 30%.

21. The Fabry-Perot etalon of claim 1 , wherein an air cavity between said concave reflecting surface and said optical fiber prevents a high drift of an optical filter waveform of said optical signal due to a change in temperature.

22. The Fabry-Perot etalon of claim 3, wherein an end of said optical fiber is positioned at a confocal point of said plano-concave mirror, wherein said positioning of said end of said optical fiber facilitates said substantial reflection of said received optical signal back to said optical fiber.

23. A method for filtering an optical signal, comprising the steps of: providing a housing made of a material with a low coefficient of thermal expansion; connecting an optical fiber to said housing for providing an optical signal; receiving said optical signal from said optical fiber; and reflecting, by a reflecting surface, said received optical signal substantially back to said optical fiber, wherein said reflecting surface is part of said housing.

24. The method of claim 23, wherein said providing step further comprises the step of: selecting said material with a low coefficient of thermal expansion to provide said housing.

25. The method of claim 23, wherein a reflectivity of said reflecting surface is selected to be approximately 100%o.

26. The method of claim 23, further comprising the step of: selecting said reflecting surface to be a concave reflecting surface.

27. The method of claim 26, wherein said concave reflecting surface is part of a plano-concave mirror.

28. The method of claim 27, further comprising the step of: selecting a material having a low coefficient of thermal expansion to form said plano-concave mirror.

29. The method of claim 27, further comprising the step of: positioning an end of said optical fiber at a confocal point of said plano-concave mirror, wherein said positioning of said end of said optical fiber facilitates said substantial reflection of said received optical signal back to said optical fiber.

30. The method of claim 26, further comprising the step of: selecting said concave reflecting surface to have a substantially uniform radius of curvature.

31. The method of claim 23, further comprising the step of: tuning a cavity between said reflecting surface and said optical fiber to a desired wavelength by a tuner.

32. The method of claim 31 , further comprising the step of: determining a center wavelength of said cavity by selecting an angle of said tuner in said cavity.

33. The method of claim 31 , further comprising the step of: selecting a material having a low coefficient of thermal expansion to form said tuner.

34. The method of claim 23, further comprising the step of: selecting a core of said optical fiber to be of uniform width.

35. The method of claim 23, further comprising the step of: coating an end of said optical fiber facing said reflecting surface with a reflective coating.

36. The method of claim 35, further comprising the step of: selecting said reflective coating to coat said end of said optical fiber to provide a reflectivity of approximately 20%.

37. A stable Fabry-Perot etalon, comprising: a housing made of a material with a low coefficient of thermal expansion; a first mirror being part of said housing for receiving an optical signal from an optical fiber; a second mirror, wherein said second mirror is substantially parallel to said first mirror wherein said second mirror is part of said housing, wherein said first mirror provides said received optical signal to said second mirror; and a tuner for tuning a cavity between said first mirror and said second mirror.

38. The stable Fabry-Perot etalon of claim 37, wherein said etalon is communicatively comiected to an optical fiber for receiving said optical signal from said optical fiber.

39. The stable Fabry-Perot etalon of claim 38, wherein said optical signal from said optical fiber is provided to a collimating lens prior to being provided to said first mirror.

40. The stable Fabry-Perot etalon of claim 39, wherein said collimating lens coUimates said optical signal received from said optical fiber and provides the collimated signal to said first mirror.

41. The stable Fabry-Perot etalon of claim 37, wherein a surface of said first mirror facing said second mirror is partially coated with a reflecting coating.

42. The stable Fabry-Perot etalon of claim 37, wherein a surface of said second mirror facing said first mirror is coated with a reflecting coating. ,

43. The stable Fabry-Perot etalon of claim 41, wherein said coated surface of said first mirror has a reflectivity of approximately 20%.

44. The stable Fabry-Perot etalon of claim 42, wherein said coated surface of said second mirror has a reflectivity of approximately 100%.

45. The stable Fabry-Perot etalon of claim 37, wherein an angle of said tuner in said cavity determines a center wavelength of said cavity.

46. The stable Fabry-Perot etalon of claim 37, wherein said tuner is a tuning plate of thickness approximately 100 μm.

47. The stable Fabry-Perot etalon of claim 37, wherein said tuner is made of a material having a low thermal expansion coefficient.