Patent Application
20180364420
This invention relates to microelectromechanical systems and more particular to designs and enhancements for MEMS mirrors and optical components exploiting such MEMS mirror elements.
Wavelength division multiplexing (WDM) has enabled telecommunication service providers to fully exploit the transmission capacity of optical fibers in their core network. State of the art systems in long-haul networks now have aggregated capacities of terabits per second. Moreover, by providing multiple independent multi-gigabit channels, WDM technologies offer service providers with a straight forward way to build networks and expand networks to support multiple clients with different requirements. At the same time these technologies have evolved down through the local area networks to the subscriber access networks and into data centers to support the continuing inexorable demand for data. In order to reduce costs, enhance network flexibility, reduce spares, and provide reconfigurability many service providers have migrated away from fixed wavelength transmitters, receivers, and transceivers, to wavelength tunable transmitters, receivers, and transceivers as well as wavelength dependent add-drop multiplexer, space switches etc.
At the same time, improvements in imaging technology have had a great impact on modern medicine. Imaging is a powerful tool that allows non-invasive diagnostics, helps to plan and direct surgical interventions, and facilitates treatment monitoring. One emerging imaging techniques is Optical Coherence Tomography (OCT), which can provide high-resolution 3D images. This technique is a non-invasive and non-contact technology. In the last decade, optical coherence tomography has found applications in several medical fields, including ophthalmology, dermatology, cardiology, dentistry, neurology, and gastroenterology.
At first sight, the provisioning of wavelength tunable transmitters, receivers, and transceivers for optical telecommunications may seem to have little in common with medical imaging systems operating at video frame rates with cycling speed rates of over 1 kHz and delay ranges of more than 3.33 ps to support millimeter depth penetration using OCT. However, in both applications the requirements for smaller footprint, improved performance, and reduced cost have led to the adoption of monolithic optical circuit technologies, hybrid optoelectronic integration, and exploitation of technologies such as microelectromechanical systems (MEMS).
A common MEMS element to both is a MEMS mirror capable of deflection under electronic control. However, unlike most MEMS device configurations where the MEMS is used to simply switch between two positions in these devices the state of MEMS is important in all transition positions. Additionally, in the optical system designs described according to embodiments of the invention the MEMS mirror rotates in-plane. The characteristics of the MEMS determines the characteristics of the whole optical delay line system and by that the OCT system in one and in the other the number of wavelength channels and the dynamic wavelength switching capabilities in the other. The role of the MEMS is essential and it is responsible for altering the paths of the different wavelengths in either device.
Accordingly, it would be beneficial to improve the performance of such MEMS and thereby the performance of the optical components and optical systems they form part of. Beneficially, the inventors have established a range of improvements to the design and implementation of such MEMS mirrors as well as optical waveguide technologies supporting the extension of these device concepts in the mid-infrared for optical spectroscopy for example.
Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures.
It is an object of the present invention to mitigate limitations in the prior art relating to microelectromechanical systems and more particular to designs and enhancements for MEMS mirrors and optical components exploiting such MEMS mirror elements.
In accordance with an embodiment of the invention there is provided a device comprising a microelectromechanical element, the microelectromechanical element having at least a front surface and a back surface, and an optical circuit disposed adjacent to the microelectromechanical element having a coupling surface having a profile matching the front surface.
In accordance with an embodiment of the invention there is provided a device comprising:
In accordance with an embodiment of the invention there is provided a device comprising:
In accordance with an embodiment of the invention there is provided a device comprising:
Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures.
Embodiments of the present invention will now be described, by way of example only, with reference to the attached Figures, wherein:
The present invention is directed to microelectromechanical systems and more particular to designs and enhancements for MEMS mirrors and optical components exploiting such MEMS mirror elements.
The ensuing description provides exemplary embodiment(s) only, and is not intended to limit the scope, applicability or configuration of the disclosure. Rather, the ensuing description of the exemplary embodiment(s) will provide those skilled in the art with an enabling description for implementing an exemplary embodiment. It being understood that various changes may be made in the function and arrangement of elements without departing from the spirit and scope as set forth in the appended claims.
1. APPLICATIONS
1A: Wavelength Tunable Optical Source
As noted supra wavelength tunable optical sources and/or receivers have significant benefit in the provisioning of transmitters, receivers, and transceivers within todays optical communication networks and evolving requirements for optical networks with dynamic wavelength allocation, reduced installation complexity, single line card designs, and reconfigurability. Within the prior art several approaches have been employed to date and whilst these have demonstrated high performance transmitters they suffer limitations such as assembly complexity, achievable performance, and cost. Two such prior art approaches are depicted in second and third images 100B and 100C respectively in comparison to a standard fixed wavelength laser source in first image 100A.
In first image 100A a fixed wavelength laser source is depicted in a dual-in line (DIL) package configuration 115 and comprises monitor photodiode (not identified for clarity) and laser diode die 111 mounted upon a chip carrier 112 which comprises a thermistor (not identified for clarity) for monitoring the temperature as the laser diode die 111 has a fast wavelength versus temperature profile. The output of the laser diode die 111 is coupled via an optical lens—optical isolator assembly 113 such that is focused at a location 113 wherein the optical fiber within a ferrule assembly 114, for example, is positioned and assembled to couple the optical signal to the network via optical fiber pigtail 116. The laser diode die 111 may, for example, be a distributed feedback (DFB) laser, a distributed Bragg reflector (DBR) laser or a monolithic externally modulated DFB laser.
Accordingly, in second image 100B a wavelength settable transmitter assembly prior to optical fiber pigtailing and sealing is depicted. As shown the assembly comprises a laser array 121, MEMS switch array 122, monitor photodiode 123 and wavelength locker 124. The wavelength locker 124 provides a means of locking the laser array 121 to a predetermined grid, such as 100 GHz C-band grid of long-haul telecommunications around 1550 nm. Accordingly, the laser array 121 comprises an array of optical sources monolithically integrated into the same semiconductor die, e.g. 40 DFB lasers. The provisioning of the selected wavelength for the transmitter is determined by the provisioning of electrical drive current to the appropriate DFB laser within the laser array 121 and the switching of the appropriate MEMS switch element within the MEMS switch array 122. As such the approach is costly in that not only must a monolithic indium phosphide (InP) M-channel DFB laser array be implemented but also an array of M MEMS switches. Accordingly, in some instances the free-space optical interconnect from the laser array 121 to optical fiber (not depicted for clarity) is replaced by a wavelength division multiplexer, such as an array waveguide grating (AWG) on the same die as the laser array 121.
Third image 100C depicts an alternate wavelength tunable transmitter exploiting a an external cavity laser (ECL) configuration wherein rather than the laser diode die having two high reflectivity facets to support the required cavity oscillation to provide gain within the semiconductor device the laser diode die has one or no high reflectivity facets and forms a resonant optical cavity with one or two external mirrors. In this instance a single external mirror 131 is employed in conjunction with a semiconductor optical amplifier (SOA) die 132 that has a high reflectivity facet towards the optical fiber pigtail 135 and a low reflectivity facet towards the external mirror 131. The resultant laser output is coupled from the SOA die 132 to the optical fiber pigtail 135 via isolator 133 and lens 134. In this instance the external mirror 132 is a tunable Fabry-Perot cavity filter 131 that provides for wavelength dependent reflectivity such that the output of the assembly is wavelength specific according to the settings of the tunable Fabry-Perot cavity filter 131 allowing the emission wavelength to be adjusted. However, the characteristics of the source are now defined by the quality of the Fabry-Perot cavity filter, which even when implemented using a MEMS construction does not achieve the sidelobe rejection of the DFB approaches.
Accordingly, it would beneficial to provide a tunable wavelength transmitter which can be fabricated at reduced cost commensurate with the pricing expectations of telecom system providers and telecom original equipment manufacturers (OEMs) for high volume generalized deployment within optical access networks, local area network, and data centers for example. Accordingly, the inventors have established a hybrid circuit implementation exploiting an ECL configuration utilizing an InGaAsP SOA, for 1310 nm or 1550 nm wavelength ranges, in conjunction with a silicon MEMS wavelength selective reflector (MEMS-WSR). As depicted in fourth image 100D the approach exploits a silicon based MEMS-WSR which comprises a coupling region 144 for coupling between the SOA 145, a tunable MEMS mirror 141, and an array of Bragg reflectors 143. The optical signals are coupled between the coupling region 144 and the array of Bragg reflectors 143 by a planar waveguide region 142 wherein the diverging optical signals from the Bragg reflector 143 are re-focussed by the tunable MEMS mirror 141. Accordingly, as depicted in first and second schematics 150A and 150B the wavelength operation of the ECL is therefore controlled by the routing selection of the mirror 141 to a selected Bragg grating within the array of Bragg reflectors 143.
Referring to
It would be evident that in addition to wavelength tunable transmitters the approach of a MEMS mirror in conjunction with an array of Bragg reflectors may also form part of wavelength tunable receivers, reconfigurable optical add—drop multiplexers (ROADMs), wavelength selective optical switches, and other wavelength selective structures, for example.
1B: Integrated Continually Tunable Optical Delay Line
As outlined supra one of the Optical Coherence Tomography approaches is TD-OCT where a reference light signal is scanned with a variable delay and then compared with the light reflected back from the sample to measure the time of flight. A schematic representation of a basic TD-OCT system is presented in
The new optical delay line system is a miniature and new designed version of the bulk Fourier domain optical delay line system as known within the prior art, see for example Rollins et al. in “In Vivo Video Rate Optical Coherence Tomography” (Optics Express, Vol. 3, No. 6, 21914). Within an embodiment of the invention an optical signal from integrated optical waveguide is projected directly onto the active surface of a MEMS mirror. The system is designed, according to an embodiment of the invention, to be implemented on a silicon-on-insulator (SiO2) substrate because it is a widely available and mature and flexible technology and it is easier to merge with MEMS fabrication processes.
However, unlike the majority of MEMS configurations where the MEMS device is used as switch between two positions in this device the state of the MEMS is important in all transition positions. The characteristics of the MEMS thereby determine to a large degree the characteristics of the whole optical delay line system and by that the OCT system. The role of the MEMS is to alter the paths of the different wavelengths in order to generate a new path difference between the wavelengths thereby creating the delay time. The inventors have exploited two different MEMS and the characteristics of each one are presented in schematic 300D in
First and second echelle gratings 355 and 390 respectively provide the required wavelength dispersion such that the incident optical signal to the device is split into several paths according to wavelength, as shown by the different lines in
Moreover, to avoid losses from clipping the optical signal by having reflecting surfaces smaller than the optical beam, all optical surfaces in the device were designed to be at least 3 times larger than the incident beam radius, which is defined as where the power is reduced to 1/e2 from the peak. This ensures that the system has negligible clipping losses. The MEMS Bragg mirror 380 within an embodiment of the invention consists of 5 and ½ pairs of silicon/air interfaces, with a 7.8 μm thickness, 300 μm long, and 12.46 μm wide as depicted in side view 300C in
Now referring to second schematic 400C the design outlined here is essentially the same as that depicted in schematic 300D in
This mirror shape keeps the air gap distance between the mirror and the planar waveguide fixed during the rotation of the MEMS mirror, thus keeping optical losses low and constant. This is important in order for the losses to be as uniform as possible for all delay set points. The largest losses are sustained at the air gap because of the near field diffraction from the optical waveguide into free space. In this system, because the thickness of the waveguide and hence the optical mode, is relatively large 7.8 μm, and the air gap is kept small in comparison with the optical mode, the impact of this diffraction is minimal. For the fundamental mode and a 0.98 μm air gap, the coupling between the diffracted beam and the planar waveguide is approximately 99%. Moreover, reflections are suppressed through the use of parylene antireflection coatings and by making the length of the air gap an odd multiple of one quarter of the broadband source central wavelength. This minimizes unwanted reflections through destructive interference.
Due to the architecture of the optical delay line circuit, second schematic 400C, actuation of the SC-MEMSM is required in only one angular direction, thus simplifying the actuator required, and reducing its impact on the resonant frequency on the SC-MEMSM. In addition, the comb drive has angled stator fingers, in order to ensure that the comb can sufficiently rotate without its movable fingers colliding with the stator fingers. The SC-MEMSM must provide a rotational displacement θ, e.g. 2° degrees. The required vertical displacement, d, of the comb drive is geometrically defined by Equation (1)
d=A
M tan(θ) (1)
AM is the distance between the comb drive attachment and the mirror center point, and θ is the rotational angle.
Optimal dimensions and placement for the comb drive were derived from analysis and simulation. Notably, fixing the maximal rotation to be 2°, end attaching the comb drive at 17 μm from the mirror center point the required vertical displacement of the comb drive is calculated to be less than 0.6 μm. This displacement is achieved with a minimum comb gap of 1.8 μm and 24 150 μm-long by 17 μm-wide comb fingers.
Graph 300F in
The latter problem is the curvature to the delay, which is attributed to small group velocity dispersion (second order dispersion) within the optical circuit. In high performance OCT systems where second order dispersion could limit the resolution, this effect could be mitigated with a more complex echelle grating design, in which the grating period is varied. In order to address these two issues the inventors established new device designs and their respective time delay profiles calculated.
Within these designs the calculation were made for a grating period of 5 μm, in silicon 1.44 μm, and the third grating order. The use of higher order dispersion is beneficial because it generates a larger dispersion angle, which affects positively the total path difference and thus allows the creation of longer delay difference. First schematic 400B in
First to fourth curved mirrors 460A, 465A, 470B and 475B act as the lenses of a bulk optical system and re-collimate the light inside the system. First to third flat mirrors 470A, 475A, and 485A provide folding of the structure for smaller footprint. The SC-MEMSM 480A comprises the final reflective mirror and is placed such that at this surface the optical beam has been re-focussed/re-collimated to occupy a small beam size, in this case not more than 200 μm. The radius of the curved mirrors is the same for first to fourth curved mirrors 460A, 465A, 470B and 475B. In fact the radius of these mirrors determines how large the system will be and the distance between the reflective mirrors defines the difference in the path and hence the delay. As examples two different setup are given and the delay time calculated for two different radius of curvature of the mirrors.
First graph 400D in
Subsequently additional design changes were made to yield a third generation optical time delay device, depicted in first schematic 500A in
Another design option is to implement an asymmetric design such as depicted in second schematic 500B in
The natural frequency of the SC-MEMSM devices simulated and implemented according to embodiments of the invention have a natural frequency that exceed 12 kHz. Accordingly, the delay can be scanned at frequencies up to approximately 10 kHz
1C: Optical Spectrometer
Within many fields from research to quality control to safety optical spectrometry is employed to determine and/or monitor materials either through the light reflected, transmitted, or radiated such as through photoluminscence for example. Different Materials have different optical spectra for each of these and accordingly either a composition may be determined or the presence of a material confirmed by one or more of these optical spectra. For example, carbon monoxide has absorption lines at approximately 1.6 μm, 2.4 μm, and 4.8 μm whilst methane has broader absorption peaks at approximately 1.7 μm, 2.3 μm, 3.2 μm and 7.9 μm and ammonia peaks at approximately 2 μm, 2.3 μm, 3 μm, 6 μm and 10 μm. In analytical systems the methodology is usually to scan across a range of frequencies to detect the absorption bands and then fit materials to the resulting spectra. In detection/alarm type applications the material of interest is known and hence the spectrometer needs to verify whether there is absorption or not. Accordingly, a spectrometer addressing the later application may be required to only monitor a few wavelengths.
Referring to
Similarly, second spectrometer 600B comprises an input optical waveguide 6700 that couples to a planar waveguide 6600 and subsequently to a grating 6750 and output waveguide 6900 disposed between absorbers 6950. However, in this instance the optical path from the input optical waveguide 6700 to the grating 6750 is folded by first reflector 6500 and the optical path from the grating 6750 to the output waveguide 6900 is similarly folded through second reflector 6550 and steered through SC-MEMSM 6800. The grating 6750 is similarly a semi-circular MEMS device but now rather than a mirror on the back surface there is etched a grating. Accordingly, the angle of the grating 6750 to the optical beam can be adjusted as well as the focusing optical signals may be steered by the SC-MEMSM 6800. Accordingly, the second spectrometer 6800 may provide increased resolution through the folded optical path and rotatable grating.
Within other embodiments of the invention a reflective filter structure such as described supra in respect of fourth image 100D in
2. Designs for Different Optical Waveguide Technologies
2A: 850 NM and Mid-Infrared—Silicon Carbide Core
The choice of the wavelength of operation for an OCT system is a compromise between resolution and penetration depth. Scattering tissues are usually imaged at 1.3 μm whereas in ophthalmic applications, 0.8 μm is usually preferred to resolve the details of the retina, see for example Drexler et al in “Optical Coherence Tomography: Technology and Applications” (Springer, 2008). However, it would be beneficial for broad exploitation of the integrated optical time delay circuit for this to operate in these two wavelength ranges with minimal adjustments. However, silicon waveguides are not transparent below 1.1 μm. Furthermore, for other applications such as molecular spectroscopy, for example, it would be desirable operate in the mid-infrared (mid-IR) between 3.0 μm≤λ≤5.0 μm Stoichiometric amorphous silicon nitride is transparent 0.3 μm≤λ≤11.0 μm whilst hexagonal crystalline silicon carbide transmits light 0.5 μm≤λ≤20.0 μm, see for example Palik in “Handbook of Optical Constants of Solids” (Academic Press, 1985). Both materials can be deposited through a variety of processes, which makes it easy and affordable to tailor waveguides to multiple applications. Whilst deposited materials can have optical properties that deviate from those reported for bulk materials the experimental measurements found in the literature indicate that for each of these materials these have acceptable properties for low loss optical waveguides over the desired transparency window.
Accordingly, the inventors propose a novel integrated waveguide structure supporting MEMS manufacturing, depicted in first waveguide cross-section 700A, where the core is silicon carbide 770 and the cladding layers are formed with silicon nitride 740. With the ability to deposit silicon carbide 770 in multiple stages an alternative design may implement MEMS elements such as MEMS mirror entirely from silicon carbide 770 in conjunction with silicon carbide optical waveguides. Other ceramic materials in addition to silicon carbide and silicon nitride that may be employed according to the devices being implement include silicon dioxide (SiO2), aluminum nitride (AlN), alumina (Al2O3), zirconia (ZrO2), and diamond (C).
2B: Telecommunications Window (1300 nm & 1550 nm)—Silicon Nitride Core
2B.1: Optical Waveguide Design
Referring to third waveguide cross-section 700B in
Referring to Table 1 there is depicted the calculated coupling for varying air gap with varying silicon nitride 740 core thickness. It is evident from this analysis that thinning the silicon nitride 740 core results in an increasing optical beam waist, increased coupling at an initial air gap of 200 nm, and increased air gap for a predetermined optical insertion loss limit, e.g. a 1 dB insertion loss penalty (80%). Accordingly, for an effective waveguide mode index of 1.492 the ideal anti-reflection coating for the optical waveguide to air would have a refractive index of 1.23
2B.2: MEMS Circuit Designs
Referring to
Once the optical signals have been coupled by the SC-MEMSM into the optical waveguides connecting to the Bragg gratings then the waveguide spacing should be increased in order to reduce the optical (parasitic) coupling from the desired waveguide to the adjacent waveguides. Referring to first and second graphs 900A and 900B in
Within the simulations of all waveguides a commercial Institute of Microelectronics (IME) process exploiting deep UV stepper based photolithography at 248 nm was assumed. This offers 180 nm and 200 nm minimum exclusion distances. Accordingly, Bragg gratings were modelled in both the 70 nm and 100 nm thick silicon nitride 720 cores to establish the bandwidth (Δλ) which is the wavelength spacing between the first minima of the grating transfer function which is given by Equation (2).
where δn0 is the variation in refractive index between the refractive index of the waveguide with and without the grating, λ the centre wavelength, and η the fraction of the power within the core of the waveguide. Accordingly, the resulting grating length required as a function of Δλ for varying waveguide reflectivity values are depicted for these 70 nm and 100 nm thick silicon nitride 740 cores in first and second graphs 900C and 900D respectively in
2B.3: MEMS Process Flow
Referring to first schematic 1000A in
Accordingly, referring to second schematic 1000B in
Now referring to fourth schematic 1000D in
Subsequently in sixth schematic 1000F in
Next in seventh schematic 1000G in
Now referring to eighth schematic 1000H in
In ninth schematic 1000I in
2C. Telecommunications Window (1300 nm & 1550 nm)—Silicon Core
2C.1 Optical Waveguide Design
Referring to second waveguide cross-section 700C in
However, the thickness limit of the silicon (Si) for a single-mode waveguide is 220 nm which is too thin for MEMS devices. However, at a thickness of 1 μm 5 modes exist within the silicon having modal indices of n=3.405, 3.203, 2.845, 2.281, 1.487 and accordingly a rib waveguide geometry is employed in order to select the fundamental mode. Due to the refractive indices the anti-reflection (AR) layer on the air gap of the optical waveguide and SC-MEMSM can be formed from parylene with a refractive index of 1.66. The thickness of the AR coating would be 233 nm.
Referring to Table 5 there is depicted the calculated coupling for varying air gap with varying silicon 720 core thickness. It is evident from this analysis that thinning the silicon 720 core results in a decreasing optical beam waist and decreasing coupling at an initial air gap of 200 nm. Accordingly, an increased thickness is preferred for a predetermined optical insertion loss limit, e.g. a 1 dB insertion loss penalty (80%).
As depicted in
Because of the slab waveguide there can be significant leakage (cross-coupling) between the rib waveguides if they are placed too close to one another. Accordingly, this imposes a lower limit on their separation thereby reducing the number of channels within the devices according to these embodiments of the invention. This is depicted in third and fourth images 1430 and 1440 respectively for a rib waveguide array wherein light is coupled into the central waveguide in third image 1430 and to an adjacent pair of waveguides in fourth image 1440. In each instance, power coupling is evident between the adjacent waveguides. Accordingly, in contrast to the separations of 0.50 μm and 0.75 μm within the silicon nitride design analysis in Section 2B supra the separations within the design analysis for the SOI rib waveguides were 4.50 μm and 5.5 μm respectively.
2C.2: MEMS Circuit Designs
Referring to
Now referring to
Accordingly, as depicted in
2C.3: MEMS Process Flow
Referring to first schematic 1700A in
Accordingly, referring to second schematic 1700B in
Subsequently in sixth schematic 1700F in
Now referring to eighth schematic 1700H in
Subsequently as depicted in ninth schematic 1700I the front surface of the WADER circuit is protected for wafer backside processing steps that follow. Accordingly, polyimide 750 with a thickness of 5 μm may be spin-coated onto the wafer and cured, e.g. 300° C. for 2 hours. Alternatively, photoresist or other materials may be employed to coat and protect the wafer prior to backside processing. Optionally at this point the substrate may also be thinned using Chemical Mechanical Polishing (CMP) for example.
In tenth schematic 1700K in
3. Semi-Circular MEMS Mirror (SC-MEMSM) Actuator Design
Referring to
Now referring to
Referring to
Referring to
4. SC-MEMSM Mirror Design
Within the embodiments of the invention, process flows, and variants discussed and described supra in respect of
The first class is where the rear reflecting mirror surface is a planar mirror such that the optical signals impinging upon it at an angle β° to the normal of the planar surface are reflect and propagate away at an angle β° on the other side of the normal. Such a rear reflecting planar mirror is depicted in
The second is a curved back mirror where the reflecting mirror surface has a predetermined profile such that the normal to the mirror surface varies across the surface and hence whilst locally each optical signal will reflect according to the normal at its point of incidence the overall effect of the mirror on beam is determined by the profile of the mirror and the point at which the optical beam impinges. Considering the rear reflecting planar mirror as depicted in
However, it would be evident that other profiles for the rear reflecting mirror surface may be employed according to the functionality of the overall optical circuit and the characteristics of the mirror required. For example, the rear surface may be parabolic to focus an impinging collimated beam or generate a collimated beam from an optical source. In addition, the surface could be corrugated in order to implement a movable dispersive element, e.g. an echelle grating.
As discussed supra with respect to the design and performance of the optical circuits comprising SC-MEMSM elements the size of the gap can factor significantly into this performance. In some optical circuits the SC-MEMSM mirror is employed once to set the device containing the optical circuit, e.g. setting the wavelength of a wavelength tunable transmitter at installation into the network. In others the SC-MEMSM mirror may be periodically or aperiodically set according to a resetting of the device rather than continuously scanned as occurs within the OCT device. In these instances the inventors have established a modified SC-MEMSM 2600 as depicted in
Now referring to
5. MEMS Gap Actuator
As indicated within
The MEMSM gap actuators 2710 are intended to bring the MEMS mirror 2750 closer to the fixed portion of the optical integrated circuit, e.g. facet 2810. This allows for a reduction in optical loss within the air gap. The minimum separation is defined by the fabrication process grid size utilised to create stoppers and not the separation dictated by the minimal feature size of the process. This allows the inventors to significantly reduce the size of the air gap between the mirror and the input and output waveguides when the gap is closed, and hence to minimize optical propagation losses. Within the exemplary embodiment depicted in
6. MEMS Latching Actuator
Once the MEMS mirror has been rotated to the appropriate angle for alignment it would be beneficial to lock the mirror into position allowing the electrostatic voltage to be removed and improving the optical integrated circuits performance against vibration and mechanical shock, for example. Referring to
Accordingly, the latching actuator locks the mast position and consequently immobilizes the mirror at a specific angle. Moreover, this stopping action is reinforced upon activation of the gap closer through the torsion of the mast. Within the exemplary embodiment depicted in
Whilst the latching described in respect of
Within the exemplary embodiment depicted in respect of
7. MEMS Pull-in Reduction
In many MEMS devices a phenomenon referred to as “pull-in” which describes a failure of the device through collapse of a microbeam for example in resonators or the failure of the spring forces within a MEMS element to overcome the electrostatic attraction such that oppositely charged elements snap together. Accordingly, in the prior art implementing a MEMS spring has been viewed as one solution to the issue. However, these are typically complex structures with large footprint.
Referring to
Beneficially the MEMS anchor spring according to embodiments of the invention provides for a simplification of the structure and reduces the footprint compared with prior art springs on the MEMS structure. Additionally, the MEMS anchor spring reduces elastic stress and plastic deformation of the spring as the MEMS anchor spring is only required to handle a small displacement rather than the full displacement. It also reduces the risk of short-circuits when placed close to other structures.
8. Temperature Compensation and Control
As discussed supra in respect of
This dynamic gap actuation could also be applied to others components of the WADER. For example, when the Si 720 and SiO2 730 are etched from the backside using ME/DRIE processes as depicted in the tenth and eleventh schematics 1000J and 1000K in
It would be evident that this mechanical compensation could be included within a feedback loop that would essentially be using an accurate temperature sensor to establish the correct mirror gap size and the Bragg reflector deflection. This integrated control allows for a more compact control and regulation subsystem.
Within embodiments of the invention described above in respect of
Within embodiments of the invention described above in respect of
Within embodiments of the invention described above in respect of
Specific details are given in the above description to provide a thorough understanding of the embodiments. However, it is understood that the embodiments may be practiced without these specific details. For example, circuits may be shown in block diagrams in order not to obscure the embodiments in unnecessary detail. In other instances, well-known circuits, processes, algorithms, structures, and techniques may be shown without unnecessary detail in order to avoid obscuring the embodiments.
The foregoing disclosure of the exemplary embodiments of the present invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many variations and modifications of the embodiments described herein will be apparent to one of ordinary skill in the art in light of the above disclosure. The scope of the invention is to be defined only by the claims appended hereto, and by their equivalents.
Further, in describing representative embodiments of the present invention, the specification may have presented the method and/or process of the present invention as a particular sequence of steps. However, to the extent that the method or process does not rely on the particular order of steps set forth herein, the method or process should not be limited to the particular sequence of steps described. As one of ordinary skill in the art would appreciate, other sequences of steps may be possible. Therefore, the particular order of the steps set forth in the specification should not be construed as limitations on the claims. In addition, the claims directed to the method and/or process of the present invention should not be limited to the performance of their steps in the order written, and one skilled in the art can readily appreciate that the sequences may be varied and still remain within the spirit and scope of the present invention.
This application claims the benefit as a continuation of U.S. patent application Ser. No. 15/124,259 filed on Sep. 7, 2016, which itself claims the benefit of priority as a 371 National Phase Application of PCT/CA2015/000136 filed Mar. 9, 2015, which itself claims the benefit of U.S. Provisional Patent Application 61/949,474 filed Mar. 7, 2014, the entire contents of all being incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61949474 | Mar 2014 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 15124259 | Sep 2016 | US |
| Child | 16048687 | US |
