WO2015178685A1

WO2015178685A1 - External cavity type tunable wavelength laser module for to-can packaging

Info

Publication number: WO2015178685A1
Application number: PCT/KR2015/005062
Authority: WO
Inventors: 이학규; 박준오; 서준규; 신장욱
Original assignee: (주)켐옵틱스
Priority date: 2014-05-20
Filing date: 2015-05-20
Publication date: 2015-11-26

Abstract

An external cavity type tunable wavelength laser module, according to the present invention, comprises: an external cavity type light source that generates wideband light; a light waveguide to which the wideband light output from the light source is input; a Bragg lattice formed in the light waveguide; a heater that is provided above the light waveguide having the Bragg lattice formed therein and adjusts a reflection band of the Bragg lattice by a thermo-optic effect; a direction change guide region for changing, by a predetermined angle, the direction of an optical signal obtained by adjusting the reflection band of the Bragg lattice; a 45-degree reflection part that transmits a part of the optical signal therethrough, which escapes from the light waveguide after the direction thereof is changed by the direction change guide region, and reflects the rest of the optical signal vertically upward; and a lens that makes the optical signal, which is reflected vertically upward by the 45-degree reflection part, collimated light or converged light. According to the present invention, a light waveguide having a Bragg lattice formed therein is designed in a structure in which the progress direction of a light signal can be changed, which leads to a reduction in the volume of an external cavity type laser module, thereby achieving standardized compact TO-CAN packaging, and accordingly reducing a cost.

Description

External resonator type wavelength tunable laser module for TO-CAN packaging

The present invention relates to an external resonator type wavelength tunable laser module for low cost and reliable TO-CAN packaging while enabling wavelength tunability in a wide wavelength range.

WDM (Wavelength Division Multiplexing) optical communication technology is currently applied to most backbone networks and metro networks, and transmits a plurality of high-speed signals by performing wavelength division multiplexing on a single optical fiber. Recently, efforts have been made to reduce inventory burden and operation cost while increasing the flexibility of the transmission network by using a wavelength tunable laser module in such a WDM transmission network.

Lasers utilizing the DFB (Distributed Feed Back) structure have been developed and commercialized in wavelength tunable lasers.However, the wavelength variable range of the DFB laser is narrow to 10 nm or less, so that all wavelengths within the C-band (1535 nm to 1565 nm) are supported. The disadvantage is the use of ~ 4 sets of tunable DFB laser modules. In addition, the wavelength-variable transponder using the DFB laser does not provide an efficient solution in view of reducing inventory burden because the light source is expensive and a multichannel transponder must be provided for backup. Accordingly, there is a need to develop an external resonator type wavelength variable laser module capable of varying all wavelengths of a WDM band (for example, C-band) required by one laser module.

1 is a plan view of a butterfly package which is a conventional external resonator type wavelength variable laser module, and FIG. 2 is a side view of a butterfly package which is a conventional external resonator type wavelength variable laser module, and more specifically, a laser diode chip. This is a schematic diagram of a butterfly package with butt-coupling optical waveguides. XMD packages, which are smaller than butterfly packages, basically have a similar configuration.

In the conventional external resonator type wavelength tunable laser module shown in FIGS. 1 and 2, an optical waveguide having a laser diode chip 10 for a light source positioned on the chip stem 11 and a Bragg grating 30 for wavelength tunability therein is formed. 20, a heater 40 provided above the optical waveguide 20, a beam splitter 50 for partially reflecting and partially transmitting an optical signal output from the optical waveguide 20, and transmitting the beam splitter 50. A lens 60 for focusing the optical signal, a photodiode 70 for measuring the power of the optical signal reflected by the beam splitter 50, and a temperature for setting the operating temperature of the wavelength tunable laser module regardless of the external temperature environment. It may be configured to include a sensor 81 and a thermoelectric cooler (82).

However, when the external resonator-type wavelength tunable laser module is configured in this way, the volume of the optical waveguide 20 including the Bragg grating 30 is large, which inevitably increases the volume of the entire wavelength tunable laser module. The cost of packaging a variable laser module is also high.

In general, TO-CAN packages are widely used in communication optical modules because of their low manufacturing cost and small volume compared to butterfly or XMD packages. However, for TO-CAN packaging, since the output direction of the optical signal should be vertically upward with respect to the TO stem surface on which the optical elements are placed, the direction of the optical signal emitted parallel to the TO stem surface should be changed vertically upward. There is this.

Meanwhile, the optical waveguide polymer wavelength tunable filter technique using Bragg grating is described by M.Oh et al., "Tunable wavelength filters with Bragg gratings in polymer waveguides," published in Applied Physics Letters, Nov. 1998 (no2) pp.2543-2545. Was first implemented, and the related technology was registered in 2001 US Pat.

An object of the present invention is to provide a structure in which the propagation direction of an optical signal that is not linear can be switched in an optical waveguide in which Bragg grating is formed to package optical elements constituting an external resonator type wavelength variable laser module. There is this.

In order to solve the above object, the external resonator-type wavelength tunable laser module according to the present invention, the external resonator-type light source for generating broadband light; An optical waveguide into which broadband light output from the light source is input; Bragg grating formed in the optical waveguide; A heater disposed above the optical waveguide on which the Bragg grating is formed, and configured to adjust a reflection band of the Bragg grating by a thermo-optic effect; A turning waveguide region for redirecting an optical signal obtained at a predetermined angle as the reflection band of the Bragg grating is adjusted; A 45 degree reflector which is redirected by the turning waveguide region and transmits a part of the optical signal exiting the optical waveguide and reflects the rest vertically upward; And a lens for making the optical signal reflected vertically upward by the 45 degree reflector into parallel light or converging light.

The turning waveguide region is configured to turn an optical signal obtained by adjusting the reflection band of the Bragg grating 180 degrees.

The external resonator type wavelength tunable laser module according to the present invention may further include a photodiode for measuring the power of the optical signal passing through the 45 degree reflector.

The external resonator type wavelength tunable laser module according to the present invention may further include a temperature sensor and a thermoelectric cooler, and are electrically connected to the heater, the temperature sensor and the thermoelectric cooler, and input a signal detected by the temperature sensor. It may further include a temperature control device for adjusting the heat generation of the heater and the heat absorption of the thermoelectric cooler.

The temperature sensor is provided on an upper portion of the optical waveguide, the thermoelectric cooler is provided on the lower portion of the optical waveguide.

The optical waveguide is a polymer optical waveguide made of a polymer.

The Bragg grating is a polymer Bragg grating made of a polymer, and the optical waveguide and the polymer forming the Bragg grating include a halogen element and include a functional group that is cured by ultraviolet rays or heat.

The optical waveguide and the polymer forming the Bragg grating are characterized in that the thermo-optic coefficient is -9.9 × 10 ^-4 to -0.5 × 10 ^-4 ℃ ^-1 .

The optical waveguide geometry is a rib structure, a ridge structure, an inverted rib structure, an inverted ridge structure, or a channel structure.

According to the present invention, by designing the optical waveguide in which the Bragg grating is formed in a structure that can change the traveling direction of the optical signal, it is possible to reduce the volume of the external resonator-type wavelength variable laser module, thereby packaging TO-CAN .

In addition, by bonding the optical elements constituting the external resonator-type wavelength tunable laser module according to the present invention with a planar optical waveguide, a difficult process such as alignment is eliminated, thereby facilitating work and contributing to productivity.

In addition, by using a standardized small TO-CAN package, there is an effect that can perform a stable, reproducible and reliable wavelength variable function.

1 is a plan view of a butterfly package which is a conventional external resonator type wavelength variable laser module.

2 is a side view of a butterfly package which is a conventional external resonator type wavelength variable laser module.

3 is a plan view of an external resonator type wavelength tunable laser module for TO-CAN packaging according to an embodiment of the present invention.

4 is a side view of an external resonator-type wavelength tunable laser module for TO-CAN packaging according to an embodiment of the present invention.

5 is a view showing the structure of the optical waveguide and the formation position of the Bragg grating in the external resonator type wavelength variable laser module according to the present invention.

Hereinafter, an external resonator type wavelength tunable laser module for TO-CAN packaging according to the present invention will be described in detail with reference to the accompanying drawings. The accompanying drawings are provided by way of example so as to fully convey the spirit of the present invention to those skilled in the art, the present invention may be embodied in other forms without being limited to the drawings presented below.

Unless otherwise defined in the technical and scientific terms used herein, it has the meaning commonly understood by those of ordinary skill in the art to which this invention belongs, and the gist of the invention in the following description and the accompanying drawings. The description of the known functions and configurations that may unnecessarily obscure them will be omitted.

3 is a plan view of an external resonator-type wavelength tunable laser module for TO-CAN packaging according to an embodiment of the present invention, Figure 4 is an external resonator-type wavelength variable for TO-CAN packaging according to an embodiment of the present invention One side view of the laser module.

The present invention utilizes the thermo-optic effect of an optical waveguide (more preferably, an optical waveguide made of a polymer material) to externally control an optical signal required by adjusting a wavelength band reflected from a Bragg grating (that is, a reflection band of a Bragg grating). To provide a wavelength tunable laser module for outputting, characterized in that for reducing the volume of the tunable laser module for TO-CAN packaging.

To this end, the wavelength tunable laser module according to the present invention includes an external resonator-type light source 100 for generating broadband light, an optical waveguide 200 into which the broadband light output from the light source 100 is input, and an optical waveguide 200. The Bragg grating 300 and the Bragg grating 300 are formed on the optical waveguide 200 formed thereon, and the heater 400 and Bragg grating 300 for adjusting the reflection band of the Bragg grating 300 by the thermo-optic effect. A part of the optical signal that is diverted by the turning waveguide region 250 and the turning waveguide region 250 to redirect the optical signal obtained by adjusting the reflection band at a predetermined angle and exits the optical waveguide 200. The 45 degree reflector 500 for transmitting the light and reflecting the rest vertically upward, and the lens 600 for making the optical signal reflected upward and upward by the 45 degree reflector 500 into parallel light or convergent light. It can be made, including.

The external resonator type light source 100 may be a semiconductor optical amplifier or a semiconductor laser diode chip that generates broadband light, wherein the emission surface of the light has an anti-reflection (AR) coating of 1% or less and is opposite to the emission surface. Silver may have a high-reflection (HR) coating with a reflectivity of 80% or greater.

When the light source 100 is a semiconductor laser diode chip for wideband wavelength oscillation, the semiconductor laser diode chip may include an active layer, a current blocking layer, a p-metal, and an n-metal layer where light is generated. Including a structure, the InP substrate may be formed of a combination of Group 3-5 elements, such as InGaAsP, InGaAlAs, InAlAs, or a combination of Group 2-4 elements, the active layer is a multi-quantum well or bulk It may be a bulk active structure.

An optical coupling lens (not shown) may be provided between the light source 100 and the optical waveguide 200, wherein the optical coupling lens collects the light output from the light source 100 to form the Bragg grating 300. Butt-coupling with the optical waveguide 200. More specifically, the optical waveguide 200 is composed of an upper cladding 210 and a lower cladding 220 and a core 230 through which light is transmitted, which induces total reflection. It may be input to the core 230 of the optical waveguide 200. On the other hand, the light source 100 may be provided on the chip stem 110 for physical support.

The optical waveguide 200 is a path through which broadband light output from the light source 100 is input at one end thereof and an optical signal obtained through the Bragg grating 300 is output at the other end. The optical waveguide 200 may be provided and supported on an upper portion of the substrate 1000, wherein the substrate 1000 may be a silicon substrate, a polymer substrate, a glass substrate, or the like.

The optical waveguide 200 includes a

cladding

210 and 220 and a core 230 surrounded by the

claddings

210 and 220, and the refractive index of the core 230 is higher than that of the

cladding

210 and 220. The light incident on the 230 is totally reflected at the interface between the core 230 and the

cladding

210, 220 according to the angle of incidence.

The Bragg grating 300 is formed by forming a groove having a predetermined period in the advancing direction of the light in the cladding (210, 220) or the core 230 of the optical waveguide 200, the empty space (air) of the groove to the Bragg grating Alternatively, the groove may be filled with a material such as silicon oxide or polysilicon to form the Bragg grating 300.

The periodic grooves forming the Bragg grating 300 reflect periodic wavelengths to the refractive index of the optical waveguide 200 through which light travels, thereby reflecting a wavelength determined by the spacing between the gratings. The optical wave having the center wavelength of the reflection band of the Bragg grating 300 is generated by the resonance of the wavelength reflected by the Bragg grating 300 to be re-input to the emission surface of the light source 100.

In more detail, the wavelength λ reflected by the Bragg grating 300 is determined by the lattice equation shown in Equation 1 below.

[Equation 1]

mλ = 2nΛ

In Equation 1, m is an odd number such as 1,3,5,7 indicating the order of the Bragg grating, n is the effective refractive index of the optical waveguide, Λ is the period of the Bragg grating.

Among the wideband optical signals (for example, optical signals having a central wavelength of λ1 to λn) of the multi-wavelength incident on one end of the optical waveguide 200, the Bragg grating 300 may satisfy the Bragg condition. An optical signal (for example, an optical signal having a center wavelength of λi) is partially reflected and returned to one end of the optical waveguide 200, and the optical signals of the remaining wavelengths are output to the other end of the optical waveguide 200. At this time, the optical signal reflected to one end of the optical waveguide 200 is fed back to the optical waveguide 200 in which the intensity of light is amplified in the light source (for example, a semiconductor laser diode chip) 100 and the Bragg grating 300 is formed. As a result, a laser having a narrow line width having a center wavelength of λi is oscillated and output to the other end of the optical waveguide 200.

Meanwhile, the change in Bragg reflection wavelength with temperature is derived from Equation 1 as shown in Equation 2 above.

[Equation 2]

m · dλ / dT = 2d (nΛ) / dT = λ ₀ (1 / ndn / dT + 1 / ΛdΛ / dT)

M, n and Λ of Equation 2 are the same as Equation 1, and λ ₀ is the initial reflection wavelength. That is, the amount of change in the reflection wavelength with respect to temperature is proportional to the sum of the amount of change in the effective refractive index with the change in the lattice period. For example, assuming a silicon waveguide Bragg grating whose lattice order m is 1 and the initial wavelength λ ₀ is 1550 nm, the change in the reflected wavelength with respect to temperature is 0.085 nm / K for a 12 nm variable corresponding to 16 channels at 100 GHz intervals. It can be seen that the temperature is about 142K. In the above example, the thermo-optic coefficient of silicon, Δn / ΔT, was 1.9 × 10 ⁻⁴ / K, and the change in period due to temperature was ignored.

As such, in order to adjust the reflection band of the Bragg grating 300 using the thermo-optic effect, the heater 400 is preferably provided on the optical waveguide 200 on which the Bragg grating 300 is formed.

The heater 400 generates joule heat as a predetermined electrical signal is applied to vary the temperature of the optical waveguide 200 in which the Bragg grating 300 is formed, and by the thermo-optic effect of the optical waveguide 200. The wavelength band reflected by the Bragg grating 300 is adjusted, and thus the center wavelength of the optical signal output to the other end of the optical waveguide 200 is varied.

The heater 400 may use any conventional metal heater which generates heat when electric power is applied, but preferably, such as Cr, Ni, Cu, Ag, Au, Pt, Ti, Al elements and nichrome It is preferable that it is a heater provided with the thin-film heating element selected from the group which consists of a laminated thin film which consists of alloys.

The redirecting waveguide region 250 refers to a waveguide region in which the optical signal obtained by the action of the Bragg grating 300 and the heater 400 is redirected at a predetermined angle among the entire regions of the optical waveguide 200.

As shown in FIG. 3, the turning waveguide region 250 may be configured to switch the optical signal obtained by adjusting the reflection band of the Bragg grating 300 at one time to change the advancing direction of the optical signal three times by 60 degrees. have. 3 may be considered to use three multi-mode total reflection mirrors therein.

In this case, the turning waveguide region 250 is not limited to the embodiment illustrated in FIG. 3, and may be configured to redirect the optical signal obtained by the action of the Bragg grating 300 and the heater 400 at various angles. have. However, when the optical signal obtained as the reflection band of the Bragg grating 300 is adjusted by 180 degrees by the turning waveguide region 250 has an advantage of minimizing the volume of the external resonator type wavelength variable laser module. .

The optical signal redirected by the turning waveguide region 250 exits the optical waveguide 200 and is partially transmitted by the 45 degree reflector 500 provided at the other end of the optical waveguide 200. It is reflected vertically upward.

Here, the 45 degree reflector 500 may be provided by bonding a separate 45 degree mirror to the other end of the optical waveguide 200 or may be provided by etching the optical waveguide 200 itself to have an inclined surface of 45 degrees. have. At this time, the 45-degree reflector 500 is coated on the reflecting surface of the reflector 500 to have a constant reflectance, so that the light incident on the reflector 500 is reflected and transmitted at a constant rate can do.

An optical signal transmitted through the 45 degree reflector 500 may be incident on the photodiode 700, and at this time, the photodiode 700 converts the incident optical signal into electrical energy to output the entire wavelength-variable laser module. Monitor the change.

On the other hand, the optical signal reflected by the 45 degree reflector 500 and traveling vertically upward becomes parallel light or convergent light by the lens 600 positioned above the 45 degree reflector 500. Specifically, when the focal length of the lens 600 is at the 45 degree reflector 500, the light becomes parallel light, and when the focal length of the lens 600 is farther than the distance from the 45 degree inclined plane to the lens 600. Become a converged light. In this case, the optical signal collected by the lens 600 may be incident on an optical fiber (not shown) positioned outside the wavelength tunable laser module. On the other hand, the shape or focal length of the lens 600 may be variously selected in consideration of the coupling loss to the optical fiber.

As described above, in the external resonator type wavelength tunable laser module according to the present invention, the reflection band of the Bragg grating 300 is controlled by the thermo-optic effect of the optical waveguide 200 according to the heat supply of the heater 400. Accordingly, the wavelength of the output optical signal can be varied. In this case, in order to cause a more efficient and accurate thermo-optic effect, it is preferable to include a temperature sensor 810 and a thermoelectric cooler 820 in the wavelength tunable laser module.

The temperature sensor 810 is preferably provided on the upper portion of the optical waveguide 200 to measure the temperature of the optical waveguide 200 in real time to adjust the current applied to the heater 400. The temperature sensor 810 may be any conventional temperature sensor whose electrical property (voltage, resistance or current amount) is changed by heat. For example, the temperature sensor 810 may include a thermistor.

Thermoelectric cooler 820 is preferably provided in the lower portion of the optical waveguide 200 to control the temperature change of the optical waveguide 200 independently of the external temperature environment so that the optical waveguide 200 has a precise thermo-optic effect. Do. The thermoelectric cooler 820 may include a conventional thermoelectric element in which endotherm is generated by a predetermined electrical signal.

Both the heater 400 and the thermoelectric cooler 820 may adjust the temperature with a precision of less than 0.1 ℃, the temperature sensor 810 is preferably capable of sensing the temperature with a precision of less than 0.1 ℃.

In addition, the temperature sensor 810 and the thermoelectric cooler 820 may be further provided with a temperature control device (not shown) so that the output characteristic of the stable optical signal is displayed independently of the external temperature environment. In this case, the temperature controller is electrically connected to the heater 400, the temperature sensor 810, and the thermoelectric cooler 820, and receives a signal detected by the temperature sensor 810 to generate heat and a thermoelectric cooler of the heater 400. 820 controls the endotherm. At this time, the temperature control device may comprise a conventional microprocessor and a computer readable storage medium on which the control program is executed.

All of the above-described optical elements constituting the external resonator type wavelength tunable laser module according to the present invention may be mounted on the TO stem 1100 for physical support and TO-CAN packaging. The TO stem 1100 is preferably made of a metal having high thermal conductivity.

The thermoelectric cooler 820 may be mounted on the TO stem 1100 using UV or thermosetting polymer resin, and the substrate 1000 and the upper portion of the substrate 1000 are positioned on the thermoelectric cooler 820. The chip stem 110 and the optical waveguide 200 may also be mounted using ultraviolet rays or a thermosetting polymer resin.

Meanwhile, the electrode 900 penetrates through the TO stem 1100 and may be provided at a predetermined number and height on the left and right sides of the thermoelectric cooler 820.

In the external resonator type wavelength tunable laser module according to the present invention, the material of the optical waveguide 200 is a polymer optical waveguide which is a polymer, and the material of the Bragg grating 300 is also a polymer Bragg grating which is a polymer. This is because the polymer material has an excellent thermo-optic effect compared to other materials.

The polymer forming the optical waveguide 200 (

cladding

210, 220 and core 230) or Bragg grating 300 includes a low loss optical polymer. The low loss optical polymer contains a halogen element such as fluorine (F) or deuterium in a general polymer, and preferably includes a functional group capable of heat or ultraviolet curing.

In addition, the polymer forming the optical waveguide 200 or Bragg grating 300 preferably has a thermo-optic coefficient of -9.9 × 10 ^-4 to -0.5 × 10 ^-4 (° C. ⁻¹ ). For example, an ultraviolet curable acrylate-based polymer in which hydrogen is substituted with fluorine, a fluorine-based polyimide, a fluorine-substituted polyacrylate, a fluorine-substituted methacrylate, polysiloxane, a fluorine-based polyarylene ether, and per pulloir cich It is preferable to use a butane series polymer or the like.

5 is a view showing the structure of the optical waveguide and the formation position of the Bragg grating in the external resonator type wavelength variable laser module according to the present invention. Optical waveguide 200 is composed of cladding (210, 220) and the core 230, the geometry of the optical waveguide 200 is a rib (ridge) structure, ridge structure, inver as shown in FIG. It may be a inverted rib structure, an inverted ridge structure, or a channel structure.

The external resonator type wavelength tunable laser module according to the exemplary embodiment of the present invention illustrated in FIGS. 3 and 4 illustrates a channel structure among the geometrical structures of the optical waveguide 200, and Bragg may have a structure other than the channel structure. The grating 300 may be formed in the

cladding

210, 220 or the core 230.

On the other hand, the effective refractive index of the optical waveguide 200 is the position of the Bragg grating, the thickness of the Bragg grating, the ON / OFF ratio of the Bragg grating, the order of the Bragg grating, the refractive index of the polymer materials constituting the core and cladding and the physical shape of the core Because of the function, it is not easy to theoretically predict the wavelength of the output optical signal in the various structures shown in FIG.

Therefore, in the present invention, the optical waveguide 200 and the Bragg grating 300 are formed using a polymer, and in controlling the effective refractive index of the optical waveguide 200, the heater 400, the temperature sensor 810, and the thermoelectric cooler 820. And the temperature control device, it is possible to predictably adjust the temperature of the optical waveguide 200 in the portion where the Bragg grating 300 is formed, thereby easily fixing the center wavelength of the output optical signal to a specific wavelength and It is desirable to be able to vary.

As mentioned above, although preferred embodiment of this invention was described in detail with reference to drawings and an example, this invention is not limited to the said embodiment, The person of ordinary skill in the art within the technical idea and the scope of the present invention is understood. It is obvious that various modifications and changes are possible.

Claims

An external resonator type light source for generating broadband light;

An optical waveguide into which broadband light output from the light source is input;

Bragg grating formed in the optical waveguide;

A heater disposed above the optical waveguide on which the Bragg grating is formed, and configured to adjust a reflection band of the Bragg grating by a thermo-optic effect;

A turning waveguide region for redirecting an optical signal obtained at a predetermined angle as the reflection band of the Bragg grating is adjusted;

A 45 degree reflector which is redirected by the turning waveguide region and transmits a part of the optical signal exiting the optical waveguide and reflects the rest vertically upward; And

And a lens for making an optical signal reflected upward and upward by the 45 degree reflector into parallel light or convergent light.
The method of claim 1,

The redirecting waveguide region is an external resonator type wavelength tunable laser module, characterized in that configured to redirect the optical signal obtained by adjusting the reflection band of the Bragg grating 180 degrees.
The method of claim 1,

And a photodiode for measuring the power of the optical signal passing through the 45 degree reflector.
The method of claim 1,

A temperature sensor and a thermoelectric cooler are further included, and are electrically connected to the heater, the temperature sensor and the thermoelectric cooler, and receive a signal sensed by the temperature sensor to control the heat generation of the heater and the endotherm of the thermoelectric cooler. External resonator type wavelength tunable laser module further comprising a control device.
The method of claim 4, wherein

The temperature sensor is provided in the upper portion of the optical waveguide, the thermoelectric cooler is an external resonator type wavelength tunable laser module, characterized in that provided in the lower portion of the optical waveguide.
The method of claim 1,

The optical waveguide is an external resonator type wavelength tunable laser module, characterized in that the polymer optical waveguide made of a polymer.
The method of claim 6,

The Bragg grating is a polymer Bragg grating made of a polymer,

And the polymer forming the optical waveguide and the Bragg grating includes a halogen element, and includes a functional group that is cured by ultraviolet rays or heat.
The method of claim 7, wherein

And the polymer forming the optical waveguide and the Bragg grating has a thermo-optic coefficient of -9.9 × 10 -4 to -0.5 × 10 -4 ° C -1 .
The method of claim 1,

The optical waveguide geometry may include a rib structure, a ridge structure, an inverted rib structure, an inverted ridge structure, or a channel structure. Tunable laser module.