WO1991017470A1 - Optical modulators - Google Patents
Optical modulators Download PDFInfo
- Publication number
- WO1991017470A1 WO1991017470A1 PCT/GB1991/000704 GB9100704W WO9117470A1 WO 1991017470 A1 WO1991017470 A1 WO 1991017470A1 GB 9100704 W GB9100704 W GB 9100704W WO 9117470 A1 WO9117470 A1 WO 9117470A1
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- substrate
- optical modulator
- electrode
- ground plane
- metal
- Prior art date
Links
Classifications
-
- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/03—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on ceramics or electro-optical crystals, e.g. exhibiting Pockels effect or Kerr effect
- G02F1/035—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on ceramics or electro-optical crystals, e.g. exhibiting Pockels effect or Kerr effect in an optical waveguide structure
- G02F1/0356—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on ceramics or electro-optical crystals, e.g. exhibiting Pockels effect or Kerr effect in an optical waveguide structure controlled by a high-frequency electromagnetic wave component in an electric waveguide structure
-
- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/21—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour by interference
- G02F1/225—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour by interference in an optical waveguide structure
- G02F1/2255—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour by interference in an optical waveguide structure controlled by a high-frequency electromagnetic component in an electric waveguide structure
-
- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/29—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the position or the direction of light beams, i.e. deflection
- G02F1/31—Digital deflection, i.e. optical switching
- G02F1/313—Digital deflection, i.e. optical switching in an optical waveguide structure
- G02F1/3132—Digital deflection, i.e. optical switching in an optical waveguide structure of directional coupler type
- G02F1/3134—Digital deflection, i.e. optical switching in an optical waveguide structure of directional coupler type controlled by a high-frequency electromagnetic wave component in an electric waveguide structure
-
- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F2201/00—Constructional arrangements not provided for in groups G02F1/00 - G02F7/00
- G02F2201/12—Constructional arrangements not provided for in groups G02F1/00 - G02F7/00 electrode
- G02F2201/127—Constructional arrangements not provided for in groups G02F1/00 - G02F7/00 electrode travelling wave
Definitions
- Optical modulators are devices for modulating an optical signal, for example its phase, amplitude or frequency.
- One class of optical modulators used for high speed operation comprises a substrate of an ele ⁇ tro-optically active material having an optical waveguide and a travelling wave electrode structure in which the microwave velocity is matched the optical velocity.
- the microwave signal develops an electric field between hot and ground electrodes in a region of the waveguide so affecting its optical properties and hence influencing any optical signal co-propagating with it.
- Such modulators include phase modulators, Mach-Zehnder modulators and directional couplers.
- Such known modulators are adversely affected by moisture and are temperature sensitive.
- the modulators are therefore hermetically sealed within a robust metal housing having a laser welded lid, often with a peltier cooling element to stabilize its temperature.
- the high frequency performance of such devices has been found to be limited by dips in the optical modulation frequency spectrum.
- an optical modulator comprises a substrate of an electrooptically active material having an optical waveguide and travelling wave electrodes including a hot electrode for applying an electric field to the optical waveguide in an active region extending in substantially one direction on a first surface of the substrate characterised in that there is single ground plane electrode which extends from near opposite sides of the hot electrode and bounds each surface of the substrate which extends substantially parallel with the active region other than the first surface.
- a single ground plane which bounds each of the surfaces of the substrate which extends substantially parallel with the hot electrode prevents unwanted propagating microwave modes within the bulk substrate electrooptic material.
- icrostrip substrate modes For convenience these unwanted modes will be referred to as icrostrip substrate modes to distinguish them from the coplanar transmission line modes between the hot electrode and the coplanar ground plane travelling wave electrodes which modulate the electrooptical properties of the waveguide.
- the single ground plane of the present invention substantially confines the microstrip modes to rectangular waveguide modes.
- the single ground plane may comprise a pair of ground electrodes formed on the first surface of the substrate each electrically connected to a metal enclosure.
- a is the rectangular waveguide width
- e is the substrate dielectric constant
- c is the speed of light.
- the cut-off frequency can be made higher than previously obtainable in prior art packaged devices as there are no resonant modes coupling energy from the coplanar transmission line modes below the cut-off frequency.
- the electrical connection ' to the metal enclosure should be continuous along the length of the electrodes to confine the modes within the ground plane. This can be achieved, for example, by bridging the gap between each of the pair of ground surface electrodes to the housing by a metallic grid.
- the grid will appear continuous if the mesh size is less than about 1/10 the microwave wavelength propagating between the hot electrode and the ground plane.
- the grid may comprise closely spaced bond wires.
- the metal enclosure may be formed by metal-soldering metal bars to the base of a metal housing in which the optical modulator is to hermetically sealed.
- the optical modulator can then be fixed to the housing between the bars and the ground plane electrodes electrically connected to the bars as described above.
- the enclosure could be formed in other ways - for example by cutting a slot in a metal block.
- the ground plane electrode comprises a metallic layer on the surfaces of the substrate.
- This layer may be made in a series of separate coating operations. This structure minimises the dimensions of the single ground plane and thereby maximises the substrate mode cut-off frequency for a given substrate size by confining the microstrip modes entirely within the substrate.
- Figure 1 is a schematic cross-sectional view of a prior art, packaged optical modulator
- Figures 2 and 3 are graphs of the electrode transmission response for a Z- ⁇ ut and X-cut Mach-Zehnder in the device package of Figure 1;
- Figures 4 to 6 are schematic cross-sectional views of three embodiments of the present invention
- Figure 7 is a plan view of the submodule of Figure 5 as part of an experimental arrangement to measure the optical modulation response with frequency
- Figure 8 is of graph of the optical modulation response with frequency of the embodiment of Figures 5 and 7;
- Figure 9 is a plan view of a further embodiment of the present invention in which the substrate has a metal coated ground plane; and Figure 10 is a graph of the optical modulator response with frequency of the embodiment of Figure 9.
- a prior art Mach-Zehnder optical modulator 2 comprises a Z-cut lithium niobate substrate 4 in which are formed in its upper surface 6 waveguides 8 and asymmetic electrodes for applying a modulated electric field across the waveguides 8, namely a ground plane electrode 10 and a hot electrode 12.
- the dimensions of the waveguides and electrodes are exaggerated for clarity.
- the substrate is fixed in a metallic sub-module 14 the ground electrode 10 being electrically tied to the sub-module 14 by a series of 10 ohm grounding resistors 16 of which only one is shown.
- the submodule is mounted on a peltier cooling element 18 fixed to the base of a robust metallic device package 20 and hermetically sealed within the package 20 by a lid 22.
- the submodule housing contains dry nitrogen gas to provide a stable environment for the optical modulator 2.
- R. F. feed lines 24 is shown coupled to the hot electrode 12.
- the optical signal is coupled to the waveguides 8 via feedthrough (not shown) perpendicular to cross-sectional view of Figure 1.
- Figure 2 shows the electrode transmission response of the Mach-Zehnder modulator of Figure 1.
- Resonant ' dips' 30 enter the spectrum at about 3 GHz. This is due to exitation of unwanted substrate modes removing power from the coplanar transmission line mode.
- Figure 3 shows the resonant dips in an X-cut Mach-Zehnder optical modulator in the device package of Figure 1.
- an optical modulator 30 has the same waveguides 8 and electrodes 10 and 12 as the prior art modulator of Figure 1.
- a single ground plane electrode is provided which extends from near both sides of the hot electrode and bounds each side, 32, 34 and 36, of the substrate which extends substantially parallel with the active region of the hot electrode 12.
- the ground plane comprises a further surface electrode 38 and the side walls 40, 44 base 42 of a slot cut in a metal block 46, inthis case copper.
- a unitary ground plane is formed by means of a closely spaced ( ⁇ 1mm) bond wires 47 coupling the electrodes 10 and 38 to the block 46.
- Other means of forming the electrical connections can be used, for example using a fine wire mesh (' gilder grid' ).
- the block 46 is mounted on a peltier cooling element 18 fixed to the base of a robust metallic device package 20 and hermetically sealed within the package 20 by a lid 22 as in the Figure 1 embodiment.
- an optical modulator 30 has a single ground electrode comprising gold plated metal bars 50 and 52 metal soldered to the base of a metal submodule housing 54. Electrical connections are made between the electrodes 10 and bars 52 and electrode 38 and bar 50 by metal bond wires (see Figure 7) as in the Figure 4 embodiment. Other materials way be used for the metallic bars may be used to form the ground plane electrode.
- the bars 52 have interposed a lithium niobate lead-in board 56 and a termination printed circuit board 58 which terminates the electrode transmission line in its characteristic impedance by means of two 50 ohm, thick film resistors 60 connected in parallel and a dc current blocking capacitor 62 to allow for dc biasing of the electrode.
- FIG 8 shows the optical modulation response of the device of Figures 5 and 7, that the cut-off frequency is increased by about 3GHz, the first resonant dip occurring at 7GHz.
- the -3dB optical modulation point at 4.35GHz is very close to the theoretically predicted -3dB point of 4.33 GHz from consideration of the hot electrode length and the 9GHz on bandwidth length rule applicable to lithium niobate travelling wave devices.
- An X-cut lithium niobate Mach-Zehnder optical modulator was found to have an overall smoother roll off as the frequency increases and does not show a 1 dB roll off in the DC to 100 MHz region typical of Z-cut devices.
- a further embodiment of the present invention comprises the same optical modulator 30 in which the single ground plane is provided by all-round metallisation 64 deposited on the substrate 30 and electrically connecting the ground plane surface electrodes 10 and 38. This provides a ground plane of minimum dimensions and therefore maximum cut-off frequency for a given substrate size.
- Figure 9 is an example of a Z-cut lithium niobate Mach-Zehnder optical modulator having all-round metallisation 70 of aluminium about a lithium niobate substrate 72 portions of which form upper surface ground electrodes 74 and 76 close to a hot electrode 78 (not separately visible on this scale).
- the widths and gaps of the symmetic, coplanar active regions are 27 ⁇ m and 9 ⁇ m, respectively and chosen to match the optical guide geometry of Z-cut Mach-Zender devices.
- the RF lead-in 82, active region 80 and lead-out 84 have a characteristic impedance maintained throughout at approximately 22 ohms to reduce the affect the reflections from impedance mismatches.
- the width of the device is 2mm to push the cut-off frequency for the substrate modes to at least 11.5 GHz.
- Figure 10 shows the optical modulation response measured from 40 MHz to 20 GHz.
- the -3dB optical modulation bandwidth was measured at 11.6 GHz and the DC switching voltage was measured at 7.3V into a 20 ohm termination resistance.
- a bandwidth of 11.6 GHz appeared to indicate that the bandwidth-length rule at 9 GHz. cm had been broken, but in fact the performance was enhanced slightly by the impedance structure of the electrodes and package, where the resistive termination of 20 ohms was slightly lower than the characteristic impedance of the electrodes, estimated at 22 ohms.
- the first package resonance occurred at approximately 13 GHz, slightly above the substrate mode design cut off frequency of 11.5 GHz.
- the rather high switching voltage of 12.8V may be reduced further by fabricating the device on X-cut lithium niobate.
- the present invention is not limited to the above specific embodiments but is applicable to other types of optical modulators employing travelling wave electrodes.
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- Physics & Mathematics (AREA)
- Nonlinear Science (AREA)
- Electromagnetism (AREA)
- General Physics & Mathematics (AREA)
- Optics & Photonics (AREA)
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Ceramic Engineering (AREA)
- Crystallography & Structural Chemistry (AREA)
- Optical Modulation, Optical Deflection, Nonlinear Optics, Optical Demodulation, Optical Logic Elements (AREA)
- Lasers (AREA)
Abstract
Description
Claims
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GB909009895A GB9009895D0 (en) | 1990-05-02 | 1990-05-02 | Optical modulators |
GB9009895.5 | 1990-05-02 |
Publications (1)
Publication Number | Publication Date |
---|---|
WO1991017470A1 true WO1991017470A1 (en) | 1991-11-14 |
Family
ID=10675368
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
PCT/GB1991/000704 WO1991017470A1 (en) | 1990-05-02 | 1991-05-02 | Optical modulators |
Country Status (7)
Country | Link |
---|---|
EP (1) | EP0527173A1 (en) |
JP (1) | JPH05509415A (en) |
AU (1) | AU7778091A (en) |
CA (1) | CA2081663A1 (en) |
GB (1) | GB9009895D0 (en) |
IE (1) | IE911467A1 (en) |
WO (1) | WO1991017470A1 (en) |
Cited By (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP1341027A2 (en) * | 2002-02-07 | 2003-09-03 | Fujitsu Limited | Optical modulator module and optical modulator |
EP1574894A1 (en) * | 2004-03-11 | 2005-09-14 | Avanex Corporation | System for reducing the electrical return loss of a lithium niobate travelling wave optical modulator with low characteristic impedance |
US6950218B2 (en) | 2003-12-17 | 2005-09-27 | Fujitsu Limited | Optical modulator |
US7856155B2 (en) | 2005-09-30 | 2010-12-21 | Sumitomo Osaka Cement Co., Ltd. | Light modulator and its fabrication method |
Families Citing this family (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5991491A (en) * | 1996-11-08 | 1999-11-23 | Nec Corporation | Optical waveguide type device for reducing microwave attenuation |
Citations (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO1989006812A1 (en) * | 1988-01-19 | 1989-07-27 | E.I. Du Pont De Nemours And Company | Waveguide structure using potassium titanyl phosphate |
-
1990
- 1990-05-02 GB GB909009895A patent/GB9009895D0/en active Pending
-
1991
- 1991-05-01 IE IE146791A patent/IE911467A1/en unknown
- 1991-05-02 CA CA 2081663 patent/CA2081663A1/en not_active Abandoned
- 1991-05-02 JP JP50824991A patent/JPH05509415A/en active Pending
- 1991-05-02 EP EP19910908597 patent/EP0527173A1/en not_active Ceased
- 1991-05-02 WO PCT/GB1991/000704 patent/WO1991017470A1/en not_active Application Discontinuation
- 1991-05-02 AU AU77780/91A patent/AU7778091A/en not_active Abandoned
Patent Citations (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO1989006812A1 (en) * | 1988-01-19 | 1989-07-27 | E.I. Du Pont De Nemours And Company | Waveguide structure using potassium titanyl phosphate |
Non-Patent Citations (3)
Title |
---|
ELECTRONICS LETTERS. vol. 25, no. 20, September 28, 1989, ENAGE GB pages 1382 - 1383; K.KAWANO ET AL.: 'New travelling-wave electrode Mach-Zehnder optical modulator with 20 GHz bandwidth and 4-7V driving voltage at 1.52 um wavelength ' see figure 1 * |
ELECTRONICS LETTERS. vol. 26, no. 5, March 1, 1990, ENAGE GB pages 318 - 320; A.DJUPSJÖBACKA: 'Novel type of baseband phase-reversal electrode for optical modulator with linear phase response ' see abstract * |
TRANSACTIONS OF THE I.E.C.E. OF JAPAN vol. E69, no. 4, April 1986, TOKIO,JP pages 415 - 417; M.IZUTSU ET AL.: 'Design Consideration for Guided-Wave Light Modulators with Coplanar Waveguide Type Electrodes ' see figure 1 * |
Cited By (7)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP1341027A2 (en) * | 2002-02-07 | 2003-09-03 | Fujitsu Limited | Optical modulator module and optical modulator |
EP1341027A3 (en) * | 2002-02-07 | 2003-09-17 | Fujitsu Limited | Optical modulator module and optical modulator |
US6873748B2 (en) | 2002-02-07 | 2005-03-29 | Fujitsu Limited | Optical modulator module and optical modulator |
US6950218B2 (en) | 2003-12-17 | 2005-09-27 | Fujitsu Limited | Optical modulator |
EP1574894A1 (en) * | 2004-03-11 | 2005-09-14 | Avanex Corporation | System for reducing the electrical return loss of a lithium niobate travelling wave optical modulator with low characteristic impedance |
US7228014B2 (en) | 2004-03-11 | 2007-06-05 | Avanex Corporation | System for reducing the electrical return loss of a lithium niobate traveling wave optical modulator with low characteristic impedance |
US7856155B2 (en) | 2005-09-30 | 2010-12-21 | Sumitomo Osaka Cement Co., Ltd. | Light modulator and its fabrication method |
Also Published As
Publication number | Publication date |
---|---|
JPH05509415A (en) | 1993-12-22 |
EP0527173A1 (en) | 1993-02-17 |
IE911467A1 (en) | 1991-11-06 |
AU7778091A (en) | 1991-11-27 |
CA2081663A1 (en) | 1991-11-03 |
GB9009895D0 (en) | 1990-06-27 |
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