WO2006007650A1

WO2006007650A1 - Optical device

Info

Publication number: WO2006007650A1
Application number: PCT/AU2005/001067
Authority: WO
Inventors: Mike Myung-Ok Lee; Hyung Jong Lee
Original assignee: Planar Photonics Pty Ltd
Priority date: 2004-07-21
Filing date: 2005-07-21
Publication date: 2006-01-26

Abstract

An optical device to combine or separate wavelengths in wavelengths division multiplexing (WDM) communication networks is disclosed, the device including a waveguide (1, 2, 3), a first ν-shaped groove passing through the waveguide (1) and including a first facet (17) and a second facet (7) where the second facet (7) being coated in a first high reflective coating (13) to reflect an optical signal of a first wavelength and appear transparent to wavelengths other than said first wavelength. The device may further include a second ν-shaped groove passing through the waveguide (2) and including a third facet (18) and a fourth facet (9) where the fourth facet (9) being coated in a second high reflective coating (14) to reflect an optical signal of a second wavelength and appear transparent to wavelengths other than said second wavelength. Preferably, the first facet (17) and the second facet (7) are angled at between 6 to 10 degrees and 40 to 50 degrees to the vertical direction, respectively.

Description

OPTICAL DEVICE FIELD OF THE INVENTION

The present invention relates to optical communication devices, and in particular towards a device to combine or separate wavelengths for use in optical communications.

BACKGROUND OF THE INVENTION

In optical fibre communications information data can be modulated to optical signals of several wavelengths and transmitted through optical fibre. For example, upward data communication signals can be transmitted using 1310nm wavelengths, downward data signals can be transmitted using 1480nm wavelength, and video stream signals can be transmitted using 1550nm wavelength through a single optical fibre. That is, it is possible to use a single optical fibre to transmit various signals with each signal being transmitted over a different wavelength. However, whilst it is possible to transmit various signals down a single channel, this is of little value if they cannot be received and utilised at the receiver end. There are two methods of insuring that the received signals are capable of being used. Firstly, the system can be configured such that only a single signal is transmitted at any one time. In this way the receiver knows that it is receiving a particular signal and does not need to attempt to separate the various signals from each other. The system will obviously require communication between the receiver and transmitter so that the receiver is synchronised or at least knows when and what signal the transmitter is transmitting. In an alternative arrangement it is possible to include an intelligent sensor at the receiver end which is capable of detecting each signal and dividing these signals appropriately. This device is a complex and expensive device which may make it prohibitive in some applications.

Wave Divisional Multiplexing (WDM) is a good solution in future telecommunication networks, because it promises or offers high capacity along with flexibility of network mesh. However, a WDM system needs many wavelength related devices, in comparison with its Time Divisional Multiplexing (TDM) counterpart. The individual cost of a WDM device is high due to the extremely high precision required in WDM systems. In high-speed long-haul transmission, numerous highly reliable WDM components are required to be deployed to ensure a high quality of service. This results in high cost. As a result WDM devices are not suited for the emerging metropolitan market as Fibre-To-The-Home (FTTH) components would need to be very cheap and are thus not cost effective.

There is therefore a need to provide a cost effective alternative to allow the advantages of WDM to be enjoyed in FTTH applications. OBJECT OF THE INVENTION

It is therefore an object of this invention to provide an optical device which is able to handle signals of varying wavelengths at relatively less expensive cost. SUMMARY OF THE INVENTION

With the above object in mind the present invention provides in one aspect a device to combine or separate wavelengths including: a waveguide; at least one v-shaped channel passing through said waveguide, each said at least one v-shaped channel including a first facet and a second facet; and wherein each said second facet is coated in a respective high reflective coating, each high reflective coating applied to each second facet being selected to reflect a signal of a predetermined wavelength and allow transmission of other wavelengths.

Preferably the first facets are angled at between 6 and 10 degrees and ideally at 8 degrees, and the second facets are angled at substantially between 40 degrees to 50 degrees and ideally at 45 degrees. The device may also include at least one sensor, such as a photodiode, over the at least one channel to detect signals reflected from said second facet. Alternatively a laser transmitter may be placed over the channels to enable signals to pass in the opposite direction. In the preferred arrangement the first facets are substantively perpendicular to the waveguide and may be referred to as a V ("neu")-shaped channel. In a further aspect the present invention provides an optical device including: a waveguide; a first v-shaped channel passing through said waveguide, said first channel including a first facet and a second facet, said second facet being coated in a first high reflective coating to reflect an optical signal of a first wavelength and appear transparent to wavelengths other then said first wavelength; and a second v-shaped channel passing through said waveguide, said second channel including a third facet and a fourth facet, said fourth facet being coated in a second high reflective coating to reflect an optical signal of a second wavelength and appear transparent to wavelengths other then said second wavelength.

In a further aspect the present invention provides a device to combine or separate wavelengths including: a waveguide; a first v-shaped channel extending from a surface and through said waveguide, said first channel including a first facet and a second facet wherein said first facet is substantially perpendicular to said surface of said waveguide and said second facet is angled from said surface of said waveguide to intersect said first facet, said second facet being coated in a first high reflective coating to reflect a signal of a first wavelength and appear transparent to signals of wavelengths other than said first wavelength; and a second v-shaped channel passing through said waveguide, said second channel including a third facet and a fourth facet wherein said third facet is substantially perpendicular to said surface of said waveguide and said fourth facet is angled from said surface of said waveguide to intersect said third facet, said fourth facet being coated in a second high reflective coating to reflect a signal of a second wavelength and appear transparent to signals of wavelengths other than said second wavelength. The device could be used as a multiplexer or demultiplexer. BRIEF DESCRIPTION OF THE DRAWINGS

The object and features of the present invention will become more apparent from consideration of the following detailed description taken in conjunction with the accompanying drawings in which: Figure 1 shows a prospective view of a preferred embodiment of the present invention.

Figure 2 shows a side view of the preferred embodiment shown in Figure 1.

Figure 3 shows one method of applying the reflective coating. Figure 4 shows an alternative way of applying the reflective coating.

Figure 5 illustrates a preferred way of creating a v-shaped channel of the present invention. DETAILED DESCRIPTION OF THE DRAWINGS

Referring to the drawings, Figures 1 and 2 show the arrangement of a preferred embodiment of the present invention. This arrangement shows a v-cut

PLC (planar lightweight circuit) multiplexer/demultiplexer. This multiplexer/demultiplexer ideally includes a waveguide core extending along the length of the device to allow for transmission of the signals. In the embodiment as shown, the waveguide core is divided into three segments 1 , 2, 3. Around the waveguide core 1 , 2, 3 is the waveguide cladding 12 which can include a substrate such as quartz wafer or silicon water. The device then includes at least one v-shaped channel.

Whilst reference is made to a v-shaped channel, in the preferred embodiment the shape of the channel more closely represents the Greek Letter v ("neu"), wherein one side of the channel is relatively vertical and the other side inclined. This is exemplified in Figure 5, where it can be seen that the left side or facet of the channel is substantially vertical or perpendicular to the surface of the waveguide, and the right facet is angled from the surface to intersect the first facet. In the arrangement as shown in the figures, a first channel 10 and a second channel 11 are shown. Photodiode mountings 4, 5 are arranged above the respective v-shaped channels 10, 11 so as to allow capture of the signals. When the channel does represent the letter v the vertical edge provides a better means for alignment of the photo diode. The ability to align the photo diode with the vertical edge assists in making large scale production easier and reliable. Further, the preferred embodiment of the v-cut reduces refraction by virtue of the vertical facet or wall of the channel, thus improving the integrity of the received optical signal.

Preferably two optical fibre coupling end facets 15, 16 are also included to allow the device to be connected to optical fibre. The v-shaped channels include a first facet 17, 18 angled at about 8 degrees, and a second facet 7, 9 angled at 45 degrees. The second facet 7, 9 also includes a highly reflective coating 13, 14 which is selected to reflect signals of predetermined wavelength.

The high reflection coating 13 of the second facet 7 of the v-shaped channel 10 is selected to reflect a wavelength λ1. This reflective coating 13 is designed to allow transmission of all other wavelengths that differ from λ1. Similarly, the high reflective coating 14 which is applied to the second facet 9 of the v-shaped channel 11 is selected to reflect signals having a wavelength λ2. Again this reflective coating 14 is designed not to impede transmission of other signals having a wavelength different from λ2.

It is recognised that some loss will be encountered as signals of a differing wavelength pass through the reflective coating, however, these losses will not be substantial nor affect the working of the device. Similarly, it is understood that some signal of a wavelength expected to be reflected will pass through the reflective material. However, this will not be substantial.

In the present invention the v-shaped groove can reflect the light of a specific wavelength channel out of the wafer plane and transmit the other channel to through-waveguide within the plane, which allows for the surface mounting of VCSEL [Vertical-Cavity Surface-Emitting Laser] and photodiodes. In conventional systems a u-shaped channel is created as described below. This u-shaped groove both reflects and transmits the light within the wafer plane and it is difficult to coat the mirror on the side-wall of the cut. This could be customised by inserting a tiny thin filter in to the U-shaped groove and cured with epoxy manually. This would be expensive for mass production. The tilt of the vertical wall of the v-shaped groove can also help to eliminate the back reflection from the cut surface and can be made in two ways; namely 4°~20° rotation about wafer normal. The preferred range of tilt angle used is 4°~20°. The multilayered dielectric coating for wavelength selection, or reflective coating 14 should only be applied to the second facet 9 of the v-shaped channel. There are two main methods of achieving this as exemplified in Figures 3 and 4. Firstly, with reference to Figures 3a and 3b, the second channel 11 can be seen with first facet 8 and second facet 9 forming the channel through the waveguide 3. With reference to Figure 3a, the first facet 8 can be protected by use of a photo-resistance patterning or protective coating for filter deposition 21. Thin film deposition 22 is then applied to the device as shown in Figure 3a. Once the dielectric coating 22 has been applied then the photoresist 21 is removed. Removing of the photoresist 21 also has the effect of removing the dielectric 22 as shown Figure 3b. Accordingly, by not applying the photoresist 21 to the second facet 9, the dielectric coating 22 is able to. be applied to the second facet 9 alone.

In an alternative method as exemplified in Figure 4, rather than applying a protective coating of the device, the device is tilted at an angle equal to or slightly greater than the angle of the first facet 8. Once the device is in this arrangement, the first facet 8 is effectively "hidden" from above whilst keeping the second facet 9 "visible" from above. The dielectric may then be applied from above the device leaving a coating over the surface of the device with the exception of the first facet 8. Thus direct coating deposition of the thin film mirror on v-shaped groove is possible and the uniformity of coating can be improved by tilting the wafer, which can be 22.5° from normal direction to deposition source for the case of a

45° neu'(greek letter)-grooved mirror. This technique is not possible in conventional U-shaped grooves or channels.

In either of these arrangements the reflective material can be selectively applied to the second facet 9 of the v-shaped channel 11. If desired the coated v-shaped channel can be filled with either polymer or glass having the same index of refraction as that of the mode reflective index of the wave guide. The preselection of the reflective material allows for control of the respective signals. A first signal having a wavelength λ1 is transmitted through the first segment 1 of the waveguide core. The signal is then reflected upwards (as shown) by the reflective coating 13 applied to the second facet 7. This signal is then received by the photodiode 4. A second signal λ2 also passes through the first segment of the waveguide core. This signal also passes through the v-cut channel 10 as the reflective coating 13 is only designed to reflect signals having a wavelength λ1. As the second signal has a wavelength λ2, it passes through this reflective coating. The signal having wavelength λ2 then passes through the second segment 2 of the waveguide core to the second v-shaped channel. As the reflective coating 14 applied to the second facet 9 is designed to reflect signals having a wavelength λ2, this second signal is then reflected upwards (as shown) towards the photodiode 5.

Whilst photodiodes are preferred by the applicants it will be understood that other devices capable of detecting the signal could be used in place of the photodiode.

The angle of the second facet 7, 9 is preferably between 40 degrees to 50 degrees although differing angles can be accommodated. The applicants believe that 45 degrees does not present the most efficient design, although preferred results are also achieved when the angle of the second facet 7, 9 is between 40 to 42 degrees or 48 to 50 degrees. This enables the signals having wavelengths λ1 and λ2 to be reflected towards the respective photodiodes 4, 5. Having an angle of 45 degrees enables the photodiodes 4, 5 to be squarely placed over the v-cut channels 10, 11. The range of angles between 40 degrees to 50 degrees allows for cost effective design, whilst also preventing reflection from the photodiode 4, 5.

The device also allows for transmission of a return signal having a wavelength λ3. This return signal passes through the third segment 3 of the waveguide core, through the second channel 11 , the second segment 2 of the waveguide core, the first channel 10, and first segment 1 of the waveguide core. The signal λ3 is substantially not affected by the reflective coatings 13, 14 on the second facet 7, 9 as these reflective coatings are not designed to affect the signal having wavelength λ3. The first facet 6, 8 of the v-shaped channels 10, 11 is angled at between 6 and 10 degrees and ideally 8 degrees so as to minimise returned light power which could be reflected from the facets 6, 8 due to a difference of optical index between the respective waveguide cores and the v- shaped channels. The first photodiode 4 is designed to detect the first optical signal having a wavelength λ1 which has been reflected from the high reflection coating 13 of the second facet 7. Similarly, the second photodiode 5 is designed to detect the second optical signal having a wavelength λ2 which has been reflected from the reflected coating 14 applied to the second facet 9. Thus in operation, optical signals having a wavelength λ1 received at the optical fibre coupling point 15 can be received by the first photodiode 4. Similarly optical signals having a wavelength λ2 received at the optical fibre coupling point 15 can be received at the second photodiode 5. For return signals, optical signals having a wavelength of λ3 received at the optical fibre coupling point 16 can be transmitted through the device to the optical fibre coupling point 15. That is, optical signals having wavelengths λ1 or λ2 can be received at the respective photodiodes 4, 5 and optical signals having a wavelength λ3 can be transmitted through the whole device.

Whilst the embodiment shown in Figure 1 and Figure 2 shows only two v- shaped channels, it will be appreciated that the device may include a range of channels depending on the application for which it is envisaged. Any additional channels would require a reflective coating to be selected for a particular wavelength to enable operation as above.

The use of a v-shaped channel does present some construction problems, and conventional techniques of CMOS VLSI design are not suitable. Standard techniques involve placing a mask or resist over a wafer surface. These areas which are not covered by the resist can be removed in the etching step. It is important to be able to preferentially etch one material without significantly affecting the resist or underlying surface. This technique does however result in a U-shaped channel. A U-shaped channel will not work in the present invention and it is not feasible to create a v-shaped channel using these conventional techniques. Generally, it is very difficult to make a v-groove with optical quality using semiconductor processing technology, as it uses a planar process using a photoresist window which results in uniform etch of terrace. Dry-etch using a shadow mask or a grey-scaled photomask could be used for shaping the v- groove, but it is expensive and not a very reproducible process.

Further in conventional techniques the depth of etch typically used in semiconductor technology is at most 10um or less. About the order of 100um etch would not be envisaged due to the time it would take resulting generally in a rough surface due to a sputtering effect. In the preferred arrangement of the present invention approximately 100-250 um is preferred

The v-shaped multiplexer/demultiplexer of the preferred embodiment of the present invention described above can be manufactured by firstly taking a PLC waveguide which includes a waveguide core 24 surrounded by a cladding layer 25. v-shaped channels 26 or trenches can then be formed across the PLC waveguide. These channels may be formed by using a dicing blade 23 as shown in Figure 5. Given the preferred embodiment described above, this dicing blade should have two edges angled at 8 degrees and 45 degrees respectively. It is of course appreciated that the angle of the dicing blade will be determined by the angle of the v-shaped channel required. Once the v-shaped channel has been formed an anti reflection coating can be applied to the first facet which is angled at 8 degrees and a high reflection coating can be applied to the second facet angled at 45 degrees to 50 degrees. The reflective coating applied to the second facet should be selected to reflect signals having a pre-determined wavelength. Once the channels have been formed and encoded, a photodiode can then be mounted over each v-shaped channel to allow detection of the signals. If the mechanically cut surface of the v-shaped cut is rough, it can be smoothened through deposition of doped glass followed by flowing of the layer. The smoothness of the v-cut surface and the mechanical rigidity of the structure can be adjusted through controlling the doping profile of the layer.

The present invention can also be configured as a multiplexer by replacing the photodiode or signal detectors with a laser transmitter or other suitable transmitter device. In this arrangement the basic operation is similar with the exception that signals can originate with respective laser transmitters. The first signal having a wavelength λ2 can be transmitted from a first laser transmitter 5. The signal from this first laser transmitter 5 will be transmitted towards the second v-cut channel 11. The signal would be designed to be reflected by the reflective coating 14 on second facet 9. The signal would then pass through the second segment 2 of the waveguide and through the first v-cut channel 10, and through the first segment of the waveguide 1. The second signal having a wavelength λ1 may be transmitted from the first laser transmitter 4 to the first v-shaped channel 10. The signal having a wavelength λ1 is designed to be reflected from the reflective material 13 on the second facet 7. This signal is then reflected through the first segment 1 of the waveguide. It will be understood that in this manner the device can be configured to receive multiple signals and forward same along the single waveguide.

It will also be appreciated that whilst the above description has referred to a v-shaped channel, that the channels do not necessarily have to be v-shaped. For example, rather than coming to an intersection, the two facets could in fact join with a flat base. The necessary requirement is that the second facet 7, 9 be configured with the reflective coating which together allows for the signal having a specified wavelength to be reflected. The first facet should not impede or affect in any substantial manner the signals.

Similarly, the channels need not run the width of the entire device. Rather they need only cover that portion of the waveguide so as to enable the signal having the pre-determined wavelength to be reflected.

FTTH enables service providers to offer a variety of communications and entertainment services, including carrier-class telephony, high-speed Internet access, broadcast cable television, direct broadcast satellite (DBS) television, and interactive, two-way video-based services. The present invention enables all of these services to be provided over a passive optical distribution network via a single optical fibre to the home. In addition, the present invention enables a FTTH solution based on wavelength division multiplexing (WDM), or a λ-based architecture, and allows for additional flexibility and adaptability to support future services. The present device allows for design of passive network, rather than active components thus dramatically minimizing network maintenance cost and requirements. It also allows for a single optical fibre to be connected to a user's home, yet still provide the services desired by that user in a cost effective manner.

Claims

CLAIMS:

1. An optical device to combine or separate wavelengths including: a waveguide; at least one v-shaped channel passing through said waveguide, each said at least one v-shaped channel including a first facet and a second facet; and wherein each said second facet is coated in a respective high reflective coating, each high reflective coating applied to each second facet being selected to reflect a signal of a predetermined wavelength and allow transmission of other wavelengths.

2. A device as claimed in claim 1 wherein said first facet is substantially perpendicular to said waveguide.

3. A device as claimed in claim 1 , wherein said first facets are substantially angled at between 6 and 10 degrees and said second facets are angled at between 40 and 50 degrees.

4. A device as claimed in claim 1 , wherein said first facet is angled at substantially 8 degrees, and said second facet is angled at substantially 45 degrees.

5. A device as claimed in any one of claims 1 to 4, further including at least one sensor located over said at least one channel to detect signals reflected from said second facet.

6. A device as claimed in claim 5 wherein said sensor is a photodiode.

7. A device as claimed in any one of claims 1 to 4, further including at least one laser transmitter located over said at least one channel to enable signals to be transmitted onto said second facet.

8. An optical device including: a waveguide; a first v-shaped channel passing through said waveguide, said first channel including a first facet and a second facet, said second facet being coated in a first high reflective coating to reflect an optical signal of a first wavelength and appear transparent to wavelengths other then said first wavelength; and a second v-shaped channel passing through said waveguide, said second channel including a third facet and a fourth facet, said fourth facet being coated in a second high reflective coating to reflect an optical signal of a second wavelength and appear transparent to wavelengths other then said . second wavelength.

9. A device as claimed in claim 8 wherein said first facet and said third facet are relatively perpendicular to said waveguide.

10. A device as claimed in claim 8, wherein said first facet and said third facet are angled at between 6 and 10 degrees, and said second facet and said fourth facet are angled at between 40 and 50 degrees.

11. A device as claimed in claim 8, wherein said first facet and said third facet are angled at substantially 8 degrees, and said second facet and said fourth facet are angled at substantially 45 degrees.

12. A device as claimed in any one of claims 8 to 11 , further including a first sensor located over said first channel to detect signals of said first wavelength reflected from said second facet, and a second sensor located over said second channel to detect signals of said second wavelength reflected from said fourth facet.

13. A device as claimed in claim 12 wherein said first and second sensors are photodiodes.

14. A device as claimed in any one of claims 8 to 11 , further including first laser transmitter located over said first channel to enable signals of said first wavelength to be transmitted onto said second facet, and a second laser transmitter located over said second channel to enable signals of said second wavelength to be transmitted onto said fourth facet.

15. A device to combine or separate wavelengths including: a waveguide; a first v-shaped channel extending from a surface and through said waveguide, said first channel including a first facet and a second facet wherein said surface of said first facet is substantially perpendicular to said surface of said waveguide and said second facet is angled from said waveguide to intersect said first facet, said second facet being coated in a first high reflective coating to reflect a signal of a first wavelength and appear transparent to signals of wavelengths other than said first wavelength; and a second v-shaped channel passing through said waveguide, said second channel including a third facet and a fourth facet wherein said third facet is substantially perpendicular to said surface of said waveguide and said fourth facet is angled from said surface of said waveguide to intersect said third facet, said fourth facet being coated in a second high reflective coating to reflect a signal of a second wavelength and appear transparent to signals of wavelengths other than said second wavelength.

16. A multiplexer/demulitplexer as claimed in claim 15 wherein said second facet and said fourth facet are angled at between 40 and 50 degrees.