The table below summarizes the changes in accumulated other comprehensive income (loss) by component, net of tax (in thousands):

	As of December 31,
	2019			2018
Beginning accumulated other comprehensive income	$	(192	)		1,871
Actuarial loss for pension plan		(1,793	)		—
Foreign currency translation adjustments, net		(1,939	)		(2,051	)
Non-controlling interest		(15	)		(12	)
Ending accumulated other comprehensive income	$	(3,939	)	$	(192	)

As of December 31, 2019, the Company has one (1) stock-based compensation plan related to equity compensation (including equity compensation in the form of stock options, restricted stock and restricted stock units) and one (1) plan related to employee stock purchases.

	Years ended December 31,
	2019		2018
Cost of revenue	$	41	$	18
Research and product development		267		134
Selling, marketing, general and administrative		3,200		1,928
	$	3,508	$	2,080

The Company’s stock-based compensation plans are designed to attract, motivate, retain and reward employees, directors and consultants and align stockholder and employee interests.

On January 4, 2017, the Board of Directors approved, and at the 2017 Annual Meeting of Stockholders, the Company’s stockholders approved, the DASAN Zhone Solutions, Inc. 2017 Incentive Award Plan. On February 12, 2018, the Board of Directors approved an amendment to the 2017 Incentive Award Plan, which is referred to herein as the “2017 Plan Amendment”). The Company’s stockholders approved the 2017 Plan Amendment at the 2018 Annual Meeting of the Stockholders. The 2017 Incentive Award Plan, as amended by the 2017 Plan Amendment, is referred to herein as the “2017 Plan.”

The 2017 Plan authorizes the issuance of stock options, restricted stock, restricted stock units, dividend equivalents, stock payment awards, stock appreciation rights, performance bonus awards and other incentive awards. The 2017 Plan authorizes the grant of awards to employees, non-employee directors and consultants of the Company and its subsidiaries. Under the 2017 Plan, stock options may be granted at an exercise price less than, equal to or greater than the fair market value on the date of grant, except that any stock options granted to a 10% stockholder must have an exercise price equal to at least 110% of the fair market value of the Company’s common stock on the date of grant. The Board of Directors determine the term of each stock option, the option exercise price and the vesting terms. Stock options are generally granted at an exercise price equal to the fair market value on the date of grant, expiring seven (7) to ten (10) years from the date of grant and vesting over a period of four years.

The maximum number of shares of the Company’s common stock which may be granted under the 2017 Plan is the sum of (i) 600,000 shares, plus (ii) any shares subject to awards granted under the prior plan to the extent such shares become available for issuance under the 2017 Plan pursuant to its terms, plus (iii) any shares subject to an annual increase on each January 1 during the 10 year term of the 2017 Plan equal to the lesser of (x) 4% of the total shares of the Company’s common stock outstanding (on an as-converted basis) and (y) such smaller amount as may be determined by the Board of Directors in its sole discretion. The annual increase on January 1, 2019 was 663,473 shares. In addition, the following annual limitations apply: (i) the maximum aggregate number of shares of the Company’s common stock that may be subject to awards granted to any one participant during a calendar year is 4,000,000 shares; and (ii) the maximum aggregate amount of cash that may be paid to any one participant during any calendar year with respect to awards initially payable in cash is $10 million. The number of shares of the Company’s common stock that may be issued or transferred pursuant to awards granted under the 2017 Plan shall not exceed an aggregate of 8,000,000 shares.

The Company has estimated the fair value of stock-based payment awards on the date of grant using the Black Scholes pricing model, which is affected by the Company’s stock price as well as assumptions regarding a number of complex and subjective variables. These variables include the Company’s expected stock price volatility over the term of the awards, actual and projected employee option exercise behaviors, risk-free interest rate and expected dividends. The estimated expected term of options granted was determined based on historical option exercises. Estimated volatility was based on the historical volatility of the Company and the risk-free interest rate was based on the U.S. Treasury yield in effect at the time of grant for the expected life of the options. The Company does not anticipate paying any cash dividends in the foreseeable future, and therefore used an expected dividend yield of zero in the option valuation model. Forfeitures are recognized as they occur.

The weighted average assumptions used to value option grants for the year ended December 31, 2019 and 2018 are as follows:

	Years ended December 31,
	2019			2018
Expected term (years)		5.85			4.88
Volatility		65.72	%		81.87	%
Risk free interest rate		1.99	%		2.74	%

The weighted average grant date fair value of options granted during the years ended December 31, 2019 and 2018 were $7.22 and $6.49, respectively.

The following table sets forth the summary of option activity under the stock option program for the year ended December 31, 2019 (in thousands, except per share data):

	Options Outstanding			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term		Aggregate Intrinsic Value
Outstanding as of December 31, 2018		1,744		$	8.00
Granted		470			10.36
Canceled/Forfeited		(128	)		9.83
Expired		(39	)		8.32
Exercised		(35	)		6.22
Outstanding as of December 31, 2019		2,012			8.47		7.36		2,418
Vested and expected to vest at December 31, 2019		2,012			8.47		7.36		2,418
Vested and exercisable at December 31, 2019		946			7.47		5.74		1,684

The aggregate intrinsic value represents the total pretax intrinsic value, based on the Company’s closing stock price as of December 31, 2019 of $8.86 per share which would have been received by the option holders had the option holders exercised their options as of that date.

The aggregate intrinsic value of awards exercised during the years ended December 31, 2019 and 2018 were $0.2 million and $0.6 million, respectively.

As of December 31, 2019, there was $6.3 million of unrecognized compensation costs which are recognized over a weighted average period of three (3) years.

The following table sets forth the summary of option activity under the stock option program for the year ended December 31, 2018 (in thousands, except per share data):

	Options Outstanding			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term		Aggregate Intrinsic Value
Outstanding as of December 31, 2017		1,213		$	6.50
Granted		836			9.86
Canceled/Forfeited		(155	)		8.00
Exercised		(150	)		6.08
Outstanding as of December 31, 2018		1,744			8.00		8.65		10,378
Vested and expected to vest at December 31, 2018		1,744			8.00		8.65		10,378
Vested and exercisable at December 31, 2018		488			6.77		7.51		3,497

The following table sets forth the summary of restricted stock unit awards activity under the stock award program for the year ended December 31, 2019 (in thousands, except per share data):

	RSU Outstanding			Weighted Average Grant Date Fair Value
Non-vested as of December 31, 2018		4		$	7.50
Granted		40			12.77
Canceled/Forfeited		—			—
Vested		(33	)		13.11
Non-vested as of December 31, 2019		11			10.05

The following table sets forth the summary of restricted stock unit awards activity under the stock award program for the year ended December 31, 2018 (in thousands, except per share data):

	RSU Outstanding			Weighted Average Grant Date Fair Value
Non-vested as of December 31, 2017		5		$	7.43
Granted		35			9.66
Canceled/Forfeited		—			—
Vested		(36	)		9.56
Non-vested as of December 31, 2018		4			7.50

Total grant-date fair value of awards granted during the years ended December 31, 2019 and 2018 was $0.5 million and $0.3 million, respectively. Total fair value of awards vested was $0.4 million during both years ended December 31, 2019 and 2018.

On May 22, 2018, the stockholders of the Company approved the adoption of the DASAN Zhone Solutions, Inc. 2018 Employee Stock Purchase Plan (the “ESPP”). The ESPP replaced the DASAN Zhone Solutions, Inc. 2002 Employee Stock Purchase Plan.

The ESPP authorizes the issuance of up to 250,000 shares of the Company’s common stock. In addition, the ESPP provides for an annual increase on the first day of each calendar year beginning on January 1, 2019, and ending on and including January 1, 2028, equal to the lesser of (i) 1% of the shares outstanding on the last day of the immediately preceding calendar year and (ii) such smaller number of shares as may be determined by the Board of Directors in its sole discretion. Notwithstanding the foregoing, the number of shares of stock that may be issued or transferred pursuant to awards under the ESPP may not exceed an aggregate of 2,000,000 shares. These 2,000,000 shares have been registered pursuant to a registration statement on Form S-8 filed with the SEC on November 8, 2018. The purchase price of the shares will be 85% of the lower of the fair market value of our common stock on (a) the first trading day of the offering period or (b) the final trading day of the offering period, which would be the applicable purchase date.

The weighted average assumptions used to value option grants for the year ended December 31, 2019 included an Expected term of 0.5 years, Volatility of 66.04% and a Risk free interest rate of 2.31%. The Company recorded $149,000 and $14,000 of expense related to the ESPP for the year ended December 31, 2019 and 2018, respectively.