Dual lens coupling package method for laser and modulator chips

Abstract

The application discloses a double-lens coupling packaging method of a laser and a modulator chip, and is applied to the field of a new generation of high-speed optical devices. The coupling packaging process is divided into two focusing coupling steps by using a collimating lens and a focusing lens. The first part is coupled with the collimating lens, the photoelectric detector integrated on the modulator chip is used as a coupling feedback signal source, the three-dimensional collimating lens is used to maximize the photoelectric current, and then the collimating lens is moved along the optical axis direction to fix the offset of the laser, so that the transmitted light is converted from the focused light into the parallel collimating light. The second part is separately coupled with the focusing lens, and the coupling is performed to the maximum photoelectric current. The method provided by the application is simple in process and high in coupling efficiency.

Description

TECHNICAL FIELD

[0001] The present application relates to optical device coupling technology, in particular to a double-lens coupling packaging method of a laser and a modulator chip. BACKGROUND

[0002] In recent years, with the rapid development of optical communication industry, the modulation bandwidth of direct modulation laser cannot fully meet the use requirements of large-bandwidth equipment such as data center and cloud computing. Silicon optical modulator chips and thin film lithium niobate modulator chips, which emerged as the times require, can effectively make up for the defects of direct modulation laser. With the gradual deepening of research and development, optical devices and optical modules based on external modulation chips are becoming mature and gradually replacing the direct modulation laser market. Compared with traditional direct modulation laser chips, external modulation chips have the advantages of large bandwidth, various modulation methods (phase modulation, intensity modulation, and polarization modulation), and high integration. However, due to the limitations of the flow process, the out-of-light port mode of the external modulation chip is generally between 4 to 6 microns, which puts higher requirements on the design of the optical lens system and the coupling process. If the traditional glass single-lens coupling packaging method is still used, although the packaging steps are simple and the automation requirements are low, it cannot effectively guarantee the coupling efficiency between the laser chip and the modulator chip, and the process problems caused by small-mode-field optical interconnection are also difficult to control, which poses great challenges to production. SUMMARY

[0003] The present application provides a double-lens coupling packaging method of a laser and a modulator chip with higher coupling efficiency and simpler process.

[0004] Technical scheme: The double-lens coupling packaging method of a laser and a modulator chip provided by the present application comprises:

[0005] The laser, isolator, and modulator chip are placed and packaged according to the front-to-back position;

[0006] The collimating lens is placed between the laser and the isolator, and the defocus collimating lens focuses the transmitted light to the light-in port of the modulator chip;

[0007] The position of the collimating lens is finely adjusted so that the photoelectric current read by the photoelectric detector integrated on the modulator chip is maximum;

[0008] The collimating lens is translated along the optical axis to the laser direction by offset, wherein offset is the translation distance that can convert the focused light into parallel light obtained by simulation software through simulation;

[0009] The collimating lens is solidified at the current position;

[0010] The focusing lens is arranged between the isolator and the modulator chip, and the position of the focusing lens is finely adjusted so that the integrated photodetector on the modulator chip reads the maximum photoelectric current;

[0011] The focusing lens is cured at the current position.

[0012] Further, the method for simulation of the simulation software comprises:

[0013] In the simulation software, the laser, the collimating lens, the isolator and the photodetector are arranged in sequence from front to back;

[0014] The position of the collimating lens is adjusted so that the photodetector reads the maximum photoelectric current, and the position at this time is recorded as position 1;

[0015] The position of the collimating lens is continuously adjusted so that the collimating lens transmits light from focused light to parallel light, the position at this time is recorded as position 2, and the offset distance of position 2 compared with position 1 is recorded.

[0016] Further, the collimating lens and the focusing lens are open mold silicon lenses suitable for spot conversion.

[0017] Further, the spot of the modulator chip is 4-6um.

[0018] Further, the laser, the isolator and the modulator chip are packaged on a substrate.

[0019] Further, the collimating lens and the focusing lens are ultraviolet cured or heat cured.

[0020] Advantages: compared with the prior art, the present application has the following advantages: the present application adopts single-lens defocus coupling mode, which decomposes complex double-lens coupling into two single-lens couplings, on the one hand, makes up for the shortcomings of small single-lens coupling tolerance and low mode field matching degree, and has higher coupling efficiency, on the other hand, greatly simplifies the complexity of automatic coupling equipment, and has simpler process, thereby effectively improving production efficiency and yield. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 is a schematic diagram of the substrate structure before coupling, (a) is a top view, and (b) is a side view;

[0022] Figure 2 is a schematic diagram of the substrate structure when the collimating lens is added;

[0023] Figure 3 is a schematic diagram of the focusing state of the collimating lens;

[0024] Figure 4 is the 3dB coupling tolerance of the XYZ direction of the collimating lens in the focusing state;

[0025] Figure 5 is a collimating lens coupling simulation schematic diagram;

[0026] Figure 6 is a collimating lens focusing coupling offset schematic diagram after the collimating lens focusing coupling is completed, which converts the focused light into parallel light;

[0027] Figure 7 is a substrate structure schematic diagram when the collimating lens and the focusing lens are added;

[0028] Figure 8 is a final coupling state schematic diagram after the collimating lens and the focusing lens are coupled;

[0029] Figure 9 is a 3dB coupling tolerance in XYZ direction when the collimating lens and the focusing lens are in a focusing state;

[0030] Figure 10 is a collimating lens simulation coupling efficiency result schematic diagram;

[0031] Figure 11 is a collimating lens and focusing lens coupling simulation schematic diagram;

[0032] Figure 12 is a collimating lens and focusing lens simulation coupling efficiency result schematic diagram; DETAILED DESCRIPTION

[0033] The present application will be described in detail below with reference to the accompanying drawings and examples. The present embodiment provides a double-lens coupling packaging method for a laser and a modulator chip, which specifically comprises the following steps:

[0034] S1, place and package the laser, isolator, and modulator chip from front to back.

[0035] The laser in the present embodiment is specifically a semiconductor laser chip with a wavelength of 1550 nm, a divergence angle of 27x22°, an MFD of 2.4x3 um, and an output power of about 70 mW under working current. The modulator chip can be silicon light or thin film lithium niobate, and the mode spot is 4-6 um. In the present embodiment, the modulator chip is a mode conversion lens, and the working wavelength of the modulator chip is 1550 nm. The MFD of the input waveguide is about 4x4 um, the splitting ratio of the integrated directional coupler (DC) of the input waveguide is about 5%, the design grating coupling insertion loss is about 3dB, the on-chip integrated photodetector MPD of the modulator chip is a wide photodetector, and the responsivity is 1A / 1W. Figure 1As shown, the laser chip 1 is packaged on a substrate with gold layer electrodes (1.45X1mm) by pre-placed gold-tin solder, forming a COC (Chip on Carrier). The positive and negative electrodes of the laser chip 1 are led out to the substrate electrodes by gold wire bonding, facilitating coupling and power-on. The packaged COC and modulator chip 3 are thermally cured to an aluminum nitride substrate 5 with a size of about 18x9mm by thermally conductive silver glue, and the optical isolator 2 is attached in the middle of the COC and the modulator chip 3, forming an optical engine package. When coupling, the optical engine COC is powered by a probe (150mA), and the COC has an output power of about 30mW. At the same time, a 3.3V bias voltage is applied to the on-chip MPD 4 of the modulator chip, and the corresponding photocurrent signal is read for coupling signal feedback.

[0036] S2, place the collimating lens between the laser and the isolator, and defocus the collimating lens to focus its transmitted light to the light inlet of the modulator chip.

[0037] As shown in Figure 2 , the automatic coupling three-axis (bearing resolution 50nm) picks up the collimating lens 6 by a vacuum suction nozzle, places it about 250um in front of the laser chip 1, and defocuses the collimating lens 6 to focus its transmitted light to the light inlet of the modulator chip 3, as shown in Figure 3 .

[0038] S3, fine-tune the collimating lens position to maximize the photocurrent read by the photodetector integrated on the modulator chip.

[0039] Fine-tune the collimating lens position to maximize the MPD read current, which is 0.15mA at this time. At this time, perform linear scanning of the collimating lens in X, Y, and Z directions, and fit the corresponding Gaussian curve by stepwise reading of the feedback signal. Through the formula:

[0040] (where σ is the standard deviation of the Gaussian curve)

[0041] The 3dB coupling tolerances (half-width full peak) of the lens in X, Y, and Z directions are 4um, 3um, and 34um respectively, as shown in Figure 4 . Compare the tolerance values calculated by Zemax simulation with the 3dB tolerance values obtained by actual coupling fitting. If the X and Y direction errors are within ±0.5um and the Z error is within ±3um, it can be confirmed that the laser energy has been correctly coupled into the laser waveguide.

[0042] S4, translate the collimating lens along the optical axis towards the laser direction by offset, where offset is the translation distance obtained by simulation software that can convert the collimating lens transmitted light from focused light to parallel light.

[0043] In this embodiment, the specific method of simulation software simulation is: in the simulation software Zemax, the laser, collimating lens, isolator and photodetector are placed in order from front to back, as shown in Figure 5 , wherein ① is a 2.4x3um laser point light source, ② is a collimating lens, ③ is an isolator, and ④ is a 4x4um photodetector MFD receiving surface; the position of the collimating lens is adjusted so that the photocurrent read by the photodetector is maximum, and the position at this time is recorded as position 1; the position of the collimating lens is continuously adjusted to make the transmitted light of the collimating lens change from converging light to parallel light, and the position at this time is recorded as position 2, and the offset of position 2 compared with position 1 is recorded, and in this embodiment, offset = 40um. The collimating lens is removed, ultraviolet curing glue is applied at the corresponding position, and then the collimating lens is placed back, the collimating lens is finely adjusted again so that the MPD degree is returned to the maximum value (0.15mA), and then the collimating lens is translated along the optical axis by 40um in the direction of the laser, so that it changes from converging light to parallel light, as shown in Figure 6 . The present application first focuses the collimating lens to obtain the maximum MPD value because this position is unique, thereby ensuring that the light beam passing through the lens changes from focusing to collimation each time the lens is fixed and retreated.

[0044] S5, curing the collimating lens at the current position.

[0045] In this embodiment, ultraviolet curing is adopted, the UV lamp is turned on to cure the lens, 20% power for 10s, 60% power for 30s, and 80% power for 30s, the suction nozzle vacuum is released, and the collimating lens is packaged. It can be understood that in other embodiments, thermal curing or other curing methods can also be used.

[0046] S6, the focusing lens is placed between the isolator and the modulator chip, and the position of the focusing lens is finely adjusted so that the photocurrent read by the photodetector integrated on the modulator chip is maximum.

[0047] As shown in Figure 7 , in this embodiment, the focusing lens 7 is placed between the isolator 2 and the modulator chip 3, specifically at about 170um in front of the modulator chip 3, the position of the focusing lens 7 is finely adjusted so that the MPD read current is maximum (as shown in Figure 8 ), and at this time the MPD photocurrent degree is 0.5mA. Linear scanning is performed in X, Y and Z three-axis directions, the corresponding curves are fitted, and the 3dB coupling tolerance is calculated, as shown in Figure 9 , if the X and Y direction errors are within ±0.5um and the Z error is within ±3um, it can be confirmed that the laser energy has been correctly coupled into the laser waveguide.

[0048] S7, curing the focusing lens at the current position.

[0049] When curing, the focusing lens is moved away, the UV curing glue is dotted at the corresponding position, the focusing lens is put back, the focusing lens is finely adjusted, the MPD power is returned to the maximum value (0.5 mA), the UV lamp is turned on to cure the lens, the power is 20% for 10 s, 60% for 30 s, and 80% for 30 s, the suction nozzle vacuum is released, and the focusing lens packaging is completed. At this time, the double-lens packaging is completed.

[0050] In order to verify the effectiveness of the application, simulation verification is performed on the application. In the simulation, the laser, collimating lens, isolator and photodetector are placed in sequence from front to back, as shown in Figure 5 , the collimating lens position is adjusted so that the photodetector reads the maximum photocurrent, and the position at this time is recorded as position 1; the single-lens simulation coupling efficiency at position 1 is calculated to be about 25% Figure 10 , the collimating lens position is continuously adjusted so that the collimating lens transmits light from focused light to parallel light, the position at this time is recorded as position 2, and the focusing lens is placed between the isolator and the modulator chip, as shown in Figure 11 , ⑤ is the focusing lens, and the focusing lens position is finely adjusted so that the photodetector reads the maximum photocurrent; the simulation coupling efficiency at this time is calculated, that is, the double-lens simulation coupling efficiency, which is about 90% Figure 12 .

[0051] The actual coupling efficiency is calculated. The single-lens actual coupling efficiency CE1 is calculated by the following formula:

[0052]

[0053] In the formula, P is the laser output power, DC% is the modulator chip waveguide light splitting ratio, L is the grating coupling, and Impd1 is the maximum photocurrent read by the photodetector integrated on the modulator chip when the collimating lens is coupled.

[0054] In this embodiment, CE1 is

[0055]

[0056] The simulation coupling efficiency is 25%, and the difference between the two is small, which is within the expected range.

[0057] The calculation method of the double-lens actual coupling efficiency CE2 is:

[0058]

[0059] In the formula, Impd2 is the maximum photocurrent read by the photodetector integrated on the modulator chip when the focusing lens is coupled.

[0060] In this embodiment,

[0061]

[0062] The simulation coupling efficiency is 90%, considering the COC and the modulator chip patch process error (±5um) and material processing error (±20um), the patch cumulative error between the semiconductor laser chip light output and the modulator chip light input is up to ±30um at most, and the mold silicon lens itself has process error, which produces aberration, affects the coupling efficiency, in addition, the MPD current splitting ratio and the grating coupling efficiency in the coupling efficiency calculation formula are greatly affected by the modulator chip itself, therefore, combined with the actual production manufacturability, the result is within the expected range.

[0063] The above only discloses a preferred embodiment of the present application, and cannot limit the scope of the present application. Therefore, equivalent changes made according to the claims of the present application are still within the scope of the present application.

Claims

1. A dual-lens coupling packaging method for a laser and a modulator chip, characterized in that... include: The laser, isolator, and modulator chips are arranged and packaged from front to back; A collimating lens is placed between the laser and the isolator, and the defocused collimating lens focuses the transmitted light onto the input port of the modulator chip. Fine-tune the position of the collimating lens to maximize the photocurrent read by the photodetector integrated on the modulator chip; The collimating lens is translated along the optical axis towards the laser direction by offset, where offset is the translation distance obtained by simulation software that enables the collimating lens to convert the transmitted light from focused light into parallel light. Fix the collimating lens at the current position; The focusing lens is placed between the isolator and the modulator chip, and the position of the focusing lens is finely adjusted to maximize the photocurrent read by the photodetector integrated on the modulator chip. Fix the focusing lens at the current position.

2. The dual-lens coupling packaging method for laser and modulator chips according to claim 1, characterized in that: The simulation software performs simulations using the following methods: In the simulation software, the laser, collimating lens, isolator, and photodetector are arranged in order from front to back; Adjust the position of the collimating lens to maximize the photocurrent read by the photodetector, and record this position as position 1; Continuously adjust the position of the collimating lens so that the transmitted light from the collimating lens is converted from focused light into parallel light. Record this position as position 2 and record the offset distance of position 2 compared to position 1.

3. The dual-lens coupling packaging method for laser and modulator chips according to claim 1, characterized in that: The collimating lens and the focusing lens are open-mold silicon lenses suitable for mode conversion.

4. The dual-lens coupling packaging method for laser and modulator chips according to claim 1, characterized in that: The modulator chip has a pattern size of 4-6µm.

5. The dual-lens coupling packaging method for laser and modulator chips according to claim 1, characterized in that: The laser, isolator, and modulator chip are packaged on a substrate.

6. The dual-lens coupling packaging method for laser and modulator chips according to claim 1, characterized in that: The collimating lens and the focusing lens are cured by ultraviolet light or by heat.

Images