Ultra-compact packaged tunable laser assembly

Abstract

The external cavity tunable laser includes a gain median module that produces a broadband optical spectrum covering a predetermined wavelength range; a collimating lens that converts the diverging beam into a parallel beam; a pair of etalons that tune the frequency; an actuator that adjusts the optical path length of the external cavity; a bandpass filter that blocks one or more frequencies outside the predetermined wavelength range; a beam splitter that splits a percentage of the beam to a photodetector; a reflecting mirror for feedback to the gain median waveguide; an isolator that prevents light from reflecting back into the external cavity; and a hermetically sealed housing of less than 0.15 cubic centimeters.

Description

[Technical Field]

[0001] FIELD OF THE INVENTION This application relates to tunable lasers, and more particularly to compact packaged tunable laser assemblies. [Background technology]

[0002] background Optical transmission systems are used to carry data and / or voice communications in enterprise and telecommunications networks. Optical signals offer superior signal quality and speed, and minimize interference from external electromagnetic energy. Optical networks employing dense wavelength division multiplexing (DWDM) allow for multi-channel optical links.

[0003] Lasers are common light sources in optical networks. External cavity tunable lasers are commonly used where the optical signal can be modulated with a data signal to modulate the optical output of the light source for transmission over the optical network.

[0004] Due to their tunability in wavelength and optical power, as well as narrow linewidth, tunable lasers have a wide range of applications in telecom as well as datacom. To accommodate various applications, packaged tunable lasers in ultra-small form factors are required, such as QSFP DD, nano-ITLA (Integrated Tunable Laser Assembly), and pico-ITLA. There is no doubt that the challenge of achieving ultra-small form factors without compromising on performance is great. With time, and with the reduction of package form factors, higher performance is required. Summary of the Invention [Means for solving the problem]

[0005] overview In one embodiment, the external cavity tunable laser includes a gain median module that generates a broadband optical spectrum covering a predetermined wavelength range; a collimating lens that converts the diverging beam into a parallel beam; a pair of etalons that tune the frequency; an actuator that adjusts the optical path length of the external cavity; a bandpass filter that blocks one or more frequencies outside the predetermined wavelength range; a beam splitter that splits a percentage of the beam to a photodetector; a reflective mirror for feedback to the gain median waveguide; an isolator that prevents light from reflecting back into the external cavity; and a hermetically sealed housing of less than 0.15 cubic centimeters.

[0006] In another aspect, a method of communicating with light includes providing an external cavity tunable laser having a hermetically sealed volume of approximately 0.15 cubic centimeters; using a gain median module to generate a broadband optical spectrum covering a predetermined wavelength range; converting the diverging beam into a parallel beam using a collimating lens; tuning the frequency using a pair of etalons; adjusting the optical path length of the external cavity; bandpass filtering to block one or more frequencies outside the predetermined wavelength range; splitting a percentage of the beam to a photodetector; providing a reflective mirror for feedback to the gain median waveguide; and using an isolator to prevent light from reflecting back into the external cavity.

[0007] In another embodiment, an external cavity tunable laser is configured in an ultra-compact form factor hermetic package measuring less than 0.15 cubic centimeters in size. The tunable laser includes a gain median waveguide that generates a broadband optical spectrum covering a specified wavelength range, a collimating lens that converts the diverging beam into a parallel beam, a pair of etalons for tuning the frequency using a vernier mechanism, an actuator for adjusting the optical path length of the external cavity, a bandpass filter that blocks frequencies outside the specified wavelength range, a beam splitter that splits a small portion of the beam to a photodetector, a reflective mirror for feedback to the gain median waveguide, and an isolator that prevents light from reflecting back into the external cavity. An optical output subassembly is further attached to the housing.

[0008] Implementations of the above aspects may include one or more of the following: An integrated etalon and phase tuner, each with its own heater, is used with an ultra-compact tunable laser package. The heater can be deposited directly on the gain median waveguide to suppress stimulated Brillouin scattering, especially when the gain median is at a high bias current. The heater can be embedded on a submount to which the gain median flip-chip is attached, meaning that the gain median waveguide is in contact with the heater. Thus, the gain median chip is mounted face down. The heater can be heated with a periodic, sign, or triangular waveform to suppress the stimulated Brillouin scattering effect. This signal can also be used for wavelength locking. Due to the ultra-compact form factor, thermal isolation of each etalon and phase tuner is challenging. One implementation can achieve precise temperature control with thermal crosstalk.

[0009] The benefits of this system include one or more of the following: The assembly provides a compact, high-performance, tunable integrated laser assembly that can dramatically lower the barriers to deployment and operation of high-capacity, dense wavelength division multiplexing (DWDM) networks. Combining the laser source and modulator avoids the high cost of individual components. Integrating the source / modulator into a single hermetic package improves reliability. [Brief explanation of the drawings]

[0010] BRIEF DESCRIPTION OF THE DRAWINGS [Figure 1] 1 illustrates an exemplary top perspective view of an ultra-compact tunable laser package. [Figure 2] 1 illustrates an exemplary cross-sectional view of an ultra-compact tunable laser package. [Figure 3] 1 shows an exemplary top perspective view of a partially integrated etalon. [Figure 4] 1 shows an exemplary top perspective view of a fully integrated etalon. [Figure 5] 1 shows an exemplary top perspective view of a gain chip on a submount with the P side facing up. [Figure 6] 1 shows an exemplary top perspective view of a gain on a submount with the P side down. DETAILED DESCRIPTION OF THE INVENTION

[0011] Detailed Description The present application is directed to an ultra-small form factor tunable laser package, as seen in FIG. 1. The ultra-small form factor package enables a wide range of applications, such as nano ITLAs and pluggable optical transceivers, e.g., 400G ZR QSFP DD. The housing 102 contains the external cavity tunable laser and is less than 0.15 cubic centimeters. In one specific embodiment, the package is 8.5 mm long, 4.2 mm wide, and 4 mm high. The volume is 0.146 cubic centimeters. The housing may be hermetically sealed against humidity and other atmospheric gas conditions.

[0012] The electrical interface is configured at one end of the housing, with one row on the side or two rows on the end, and receives power and receives / outputs control information including signals.

[0013] An external cavity laser contains all components, such as 104-110 as shown in Figure 1 and 214 as shown in Figure 2, within a housing 102. Figure 1 also shows optical interfaces, such as 103, attached to the housing.

[0014] The external cavity tunable laser includes a diode gain chip 104 and a collimating lens 105 in the path of a beam emanating from the gain chip 104 in FIG. 1 or from the gain chip 204 in FIG. 2. The collimating lens 105 in FIG. 1 or the collimating lens 205 in FIG. 2 is mounted on a TEC platform 213 as shown in FIG. 2. The gain chip 104 in FIG. 1 or the gain chip 204 in FIG. 2 is mounted on a substrate 502. A gain chip-on-submount (CoS) 500 is mounted on the TEC platform 213 as shown in FIG. 2.

[0015] The external cavity tunable laser further includes a tuner subassembly including a first etalon 106, a second etalon 108, and a phase tuner 107. The first etalon 106 and the second etalon 108 may be made of the same or different materials. They may have the same or different thicknesses. The refractive index and thickness of one or both etalons 106 and 108 can be adjusted by temperature induced by a heater 301. A vernier variable mechanism is used for wavelength selection. The phase tuner 107 adjusts the optical path length of the external cavity to fine-tune the wavelength and locks the wavelength with a dither signal applied to the gain chip heater 503. A bandpass filter is attached to the phase tuner 107. A beam splitter 109 is positioned downstream of the tuner subassembly including components 106, 107, and 108. One beam travels along the optical axis to isolator 110, which prevents reflection from the optical output interface comprising component 103. The other beam from beam splitter 109 reaches monitor photodiode (MPD) 214 in Figure 2. The output signal from MPD 214 can be used for optical power monitoring and wavelength locking.

[0016] The temperature of the etalon 106 or 108 is induced by a heater 301, which can be integrated into both etalons, as shown in Figure 3. The etalon 302 is prepared so that both surfaces are parallel to each other before the heater element 301 is deposited by thin film physical deposition. The thermistor 303 is attached to the partially integrated etalon 300 by eutectic soldering or epoxy bonding. A thin gold wire 304, e.g., 15-35 microns in diameter, is bonded to the thermistor 303 and to metallized conductive pads on the etalon 302.

[0017] The etalon 400 may be further integrated with a thin-film heater 441 and a thin-film resistive temperature device (RTD) 443, as shown in FIG. 4. The electrical resistance of an RTD is about two orders of magnitude smaller than that of a thermistor, which is typically about 10 K ohms at room temperature. Moreover, the temperature coefficient of resistance of an RTD is relatively small compared to that of a thermistor. Therefore, for a fully integrated etalon 400, the contact resistance cannot be ignored. To cancel the contact resistance, the fully integrated etalon 400 uses two pairs of pads 444 and 445 for electrical contact.

[0018] A chip-on-submount (CoS) 500 is shown in Figure 5. A gain chip 501 is mounted P-side up on a submount 502. On top of the gain chip waveguide is a thin layer of resistive heater with a resistance of 50-500 ohms. This heater is connected to a metallized pad 503 for electrical connection. For wavelength locking, a sinusoidal or triangular dither signal is applied to the heater via the electrical connection.

[0019] Preferably, the tunable laser module is temperature stable to minimize drift in the cavity optical path length and / or stabilize the phase of the laser cavity. Temperature control also allows for fine tuning of frequency accuracy. In one embodiment, a lookup table can be created prior to laser operation to associate each channel of the ITU grating with the temperature T of both the laser diode and heater injection current, i.e., the median gain. Small changes in T result in small changes in the phase of the laser cavity, which can be adjusted for fine tuning of the wavelength of the cavity mode using selected wavelength peaks of the Fabry-Perot etalon.

[0020] A chip-on-submount (CoS) 600 is shown in Figure 6. A gain chip 601 is flip-chip mounted, P-side down, onto a submount 602. On top of the submount 602 and below the gain chip waveguide is a thin layer of resistive heater with a resistance of 50-500 ohms. This heater is connected to a metallized pad 603 for electrical connection. For wavelength locking, a sinusoidal or triangular dither signal is applied to the heater via the electrical connection.

[0021] The resulting external cavity tunable laser is configured in an ultra-compact, hermetic package 100 with a housing volume of less than 0.15 cubic centimeters. The tunable laser 100 includes a gain median waveguide that generates a broadband optical spectrum covering a specified wavelength range, such as the C-band or L-band; a collimating lens 105 or 205 that converts the diverging beam into a parallel beam; a pair of etalons 106 and 108 or 206 and 208 for frequency tuning using a vernier mechanism; an actuator or phase tuner 107 or 207 for adjusting the optical path length of the external cavity; a bandpass filter that blocks frequencies outside the specified wavelength range; a beam splitter that branches a small portion of the beam to a photodetector; a reflecting mirror for feedback to the gain median waveguide; and an isolator 110 or 210 that prevents reflected light from returning to the external cavity. Additionally, an optical output subassembly 103 is attached to the housing, which couples light into an optical fiber, which may be polarization-maintaining fiber or single-mode fiber.

[0022] Various operations of embodiments of the present invention are described herein. These operations may be performed by a machine using a processor, an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), or the like. In one embodiment, one or more of the described operations may constitute instructions stored on a machine-readable medium that, when performed by the machine, cause the machine to perform the described operations. The order in which some or all of the operations are described should not be construed to imply that these operations are necessarily order dependent. Alternative orders will be understood by one of ordinary skill in the art having the benefit of this description. Furthermore, it will be understood that not all operations are necessarily present in every embodiment of the present invention.

[0023] The above description of illustrated embodiments of the present invention, including what is set forth in the Abstract, is not intended to be exhaustive or to limit the embodiments to the precise forms disclosed. While specific embodiments and examples of the present invention have been described herein for illustrative purposes, various equivalent modifications are possible, as those skilled in the relevant art will recognize. These modifications can be made to embodiments of the present invention in light of the above detailed description. The terms used in the following claims should not be construed to limit the invention to the specific embodiments disclosed in the specification. Rather, the following claims should be construed in accordance with established doctrines of claim interpretation.

[0024] The above disclosure defines numerous embodiments of the present invention, which are described in detail in connection with the accompanying drawings. Those skilled in the art will appreciate that various changes, modifications, other structural arrangements, and other embodiments may be practiced under the teachings of the present invention without departing from the scope of the invention, which is defined in the following claims.

Claims

1. a gain median module that generates a broadband optical spectrum covering a predetermined wavelength range; a collimating lens that changes the diverging beam into a parallel beam; a pair of etalons for tuning the frequency; an actuator for adjusting the optical path length of the external cavity; a bandpass filter that blocks one or more frequencies outside the predetermined wavelength range; a beam splitter that splits a portion of the beam to a photodetector; a reflecting mirror for feedback to the gain median waveguide; an isolator that prevents light from reflecting back into the external cavity; a hermetically sealed housing of less than 0.15 cubic centimeters; 1. An external cavity tunable laser comprising:

2. 10. The laser of claim 1 wherein at least one of said etalons is frequency tuned using a Vernier method.

3. 10. The laser of claim 1 further comprising one or more heaters proximate said one or more etalons and phase tuner.

4. 4. The laser of claim 3, wherein at least one of the heaters is deposited directly on the gain median waveguide for wavelength locking or suppression of stimulated Brillouin scattering.

5. 5. The laser of claim 4 wherein said one of said heaters operates when said gain median is at a high bias current.

6. 4. The laser of claim 3 wherein at least one of said heaters is embedded in a submount to which said gain median module is mounted, meaning that said gain median waveguide is in contact with said heater.

7. 10. The laser of claim 1 comprising an optical output subassembly coupled to said hermetically sealed housing.

8. 4. The laser of claim 3 wherein said one or more heaters are heated in a cyclical format.

9. 9. The laser of claim 8, wherein the periodic format comprises a sign wave format or a triangular wave format.

10. 10. The laser of claim 8 wherein the one or more heaters suppress stimulated Brillouin scattering effects.

11. 10. The laser of claim 8 wherein the one or more heaters provide wavelength locking.

12. 10. The laser of claim 1, wherein the gain median module is mounted p-face down.

13. 10. The laser of claim 1, wherein said housing has a length of about 8.5 mm, a width of about 4.2 mm, and a height of about 4 mm.

14. 10. The laser of claim 1 wherein the housing has a volume of approximately 0.146 cubic centimeters.

15. providing an external cavity tunable laser having a hermetically sealed volume of approximately 0.15 cubic centimeters; using a gain median module to generate a broadband optical spectrum covering a predetermined wavelength range; Using a collimating lens to change the diverging beam into a parallel beam; Tuning the frequency using a pair of etalons; adjusting the optical path length of the external cavity; bandpass filtering to block one or more frequencies outside the predetermined wavelength range; splitting a fraction of the beam to a photodetector; providing a reflective mirror for feedback to the gain median waveguide; using an isolator to prevent light from reflecting back into the external cavity; A method of communicating by light, including

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